diff --git a/python/sglang/kernels/ops/moe/ep_moe_kernels.py b/python/sglang/kernels/ops/moe/ep_moe_kernels.py
index 20263ae3ab0c..a9911fead638 100644
--- a/python/sglang/kernels/ops/moe/ep_moe_kernels.py
+++ b/python/sglang/kernels/ops/moe/ep_moe_kernels.py
@@ -1267,6 +1267,7 @@ def ep_scatter_from_psum(
     m_indices: torch.Tensor,
     output_index: torch.Tensor,
     scale_ue8m0: bool = False,
+    expert_start: int = 0,
 ):
     BLOCK_E = 128
     BLOCK_D = 128
@@ -1315,6 +1316,8 @@ def ep_scatter_from_psum(
         output_index,
         output_index.stride(0),
         output_index.stride(1),
+        expert_start,
+        num_experts,
         topk_num=recv_topk.shape[1],
         num_warps=num_warps,
         HIDDEN_SIZE=hidden_size,
diff --git a/test/registered/kernels/ops/moe/test_ep_scatter.py b/test/registered/kernels/ops/moe/test_ep_scatter.py
new file mode 100644
index 000000000000..0fb927f3d471
--- /dev/null
+++ b/test/registered/kernels/ops/moe/test_ep_scatter.py
@@ -0,0 +1,175 @@
+import pytest
+import torch
+
+from sglang.kernels.ops.moe.ep_moe_kernels import ep_scatter_from_psum
+from sglang.test.ci.ci_register import register_cuda_ci
+
+register_cuda_ci(est_time=30, stage="base-b-kernel-unit", runner_config="1-gpu-large")
+
+dev = "cuda"
+BLOCK_D = 128
+BLOCK_E = 128
+
+
+def _build(num_tokens, num_experts, top_k, pad_frac, expert_start, seed):
+    """Route tokens to local experts, then describe the routing the way the
+    DeepEPv2 permute path does: an INCLUSIVE prefix sum over local experts, and
+    `recv_topk` holding expert ids offset by `expert_start` (-1 = padding)."""
+    g = torch.Generator(device="cpu").manual_seed(seed)
+    local_ids = torch.full((num_tokens, top_k), -1, dtype=torch.int32)
+    counts = [0] * num_experts
+    for t in range(num_tokens):
+        experts = torch.randperm(num_experts, generator=g)[:top_k].tolist()
+        for slot, e in enumerate(experts):
+            if pad_frac > 0 and torch.rand(1, generator=g).item() < pad_frac:
+                continue
+            local_ids[t, slot] = e
+            counts[e] += 1
+
+    psum = torch.tensor(counts, dtype=torch.int32).cumsum(0).to(torch.int32)
+    recv_topk = torch.where(local_ids >= 0, local_ids + expert_start, local_ids)
+    return local_ids.to(dev), recv_topk.to(dev), psum.to(dev)
+
+
+def _run(recv_topk, psum, hidden, dtype, expert_start):
+    num_tokens = recv_topk.shape[0]
+    total = int(psum[-1].item())
+    scale_hidden = hidden // BLOCK_D
+    is_fp8 = dtype != torch.bfloat16
+
+    recv_x = torch.randn(num_tokens, hidden, dtype=torch.bfloat16, device=dev).to(dtype)
+    if is_fp8:
+        recv_x_scale = torch.rand(
+            num_tokens, scale_hidden, dtype=torch.float32, device=dev
+        )
+        output_tensor_scale = torch.zeros(
+            total, scale_hidden, dtype=torch.float32, device=dev
+        )
+    else:
+        recv_x_scale = None
+        output_tensor_scale = None
+
+    output_tensor = torch.zeros(total, hidden, dtype=dtype, device=dev)
+    # m_indices is padded up to BLOCK_E; -1 marks slots no expert owns.
+    m_indices = torch.full(
+        ((total + BLOCK_E - 1) // BLOCK_E * BLOCK_E,), -1, dtype=torch.int32, device=dev
+    )
+    expert_start_loc = torch.empty_like(psum)
+    output_index = torch.empty_like(recv_topk)
+
+    # Leave expert_start at its default in the local-id case, so this exercises
+    # the call shape the DeepEPv2 permute path actually uses.
+    kwargs = {"expert_start": expert_start} if expert_start else {}
+    ep_scatter_from_psum(
+        recv_x,
+        recv_x_scale,
+        recv_topk,
+        psum,
+        expert_start_loc,
+        output_tensor,
+        output_tensor_scale,
+        m_indices,
+        output_index,
+        **kwargs,
+    )
+    return dict(
+        recv_x=recv_x,
+        recv_x_scale=recv_x_scale,
+        output_tensor=output_tensor,
+        output_tensor_scale=output_tensor_scale,
+        m_indices=m_indices,
+        expert_start_loc=expert_start_loc,
+        output_index=output_index,
+        total=total,
+    )
+
+
+def _check(out, local_ids, psum):
+    """The scatter's destination slots are chosen by atomic_add, so the order
+    within one expert is not deterministic. Assert the invariants instead — they
+    pin the result down completely apart from that order."""
+    output_index = out["output_index"]
+    total = out["total"]
+    valid = local_ids >= 0
+
+    # 1. -1 sentinel exactly on the padding lanes. The post-permute kernel gates
+    #    on this, so a stale value here silently reads a garbage row.
+    assert torch.equal(output_index < 0, ~valid)
+
+    # 2. Every valid lane lands inside its own expert's slab.
+    starts = torch.cat([torch.zeros(1, dtype=psum.dtype, device=dev), psum[:-1]])
+    e = local_ids[valid].long()
+    dst = output_index[valid].long()
+    assert torch.all(dst >= starts[e]) and torch.all(dst < psum[e])
+
+    # 3. ... and the slabs are filled exactly, with no slot used twice.
+    assert dst.numel() == total
+    assert torch.equal(torch.sort(dst).values, torch.arange(total, device=dev))
+
+    # 4. m_indices agrees with the routing, and the BLOCK_E tail stays -1.
+    assert torch.equal(out["m_indices"][dst], local_ids[valid].to(torch.int32))
+    assert torch.all(out["m_indices"][total:] == -1)
+
+    # 5. expert_start_loc has been advanced to each expert's end.
+    assert torch.equal(out["expert_start_loc"], psum)
+
+    # 6. The rows themselves arrived, scales included.
+    src = torch.nonzero(valid)[:, 0]
+    assert torch.equal(
+        out["output_tensor"][dst].view(torch.uint8),
+        out["recv_x"][src].view(torch.uint8),
+    )
+    if out["recv_x_scale"] is not None:
+        assert torch.equal(out["output_tensor_scale"][dst], out["recv_x_scale"][src])
+
+
+@pytest.mark.parametrize("num_tokens", [1, 8, 256, 4096])
+@pytest.mark.parametrize("pad_frac", [0.0, 0.3])
+@pytest.mark.parametrize("dtype", [torch.bfloat16, torch.float8_e4m3fn])
+def test_ep_scatter_from_psum(num_tokens, pad_frac, dtype):
+    num_experts, top_k, hidden = 8, 8, 512
+    local_ids, recv_topk, psum = _build(
+        num_tokens, num_experts, top_k, pad_frac, 0, seed=num_tokens
+    )
+    out = _run(recv_topk, psum, hidden, dtype, 0)
+    _check(out, local_ids, psum)
+
+
+@pytest.mark.parametrize("expert_start", [0, 8, 120])
+def test_ep_scatter_from_psum_expert_start(expert_start):
+    """`expert_start` shifts which global ids count as local. Offsetting both the
+    ids and `expert_start` must not change the result, and out-of-range ids must
+    be dropped like padding."""
+    num_tokens, num_experts, top_k, hidden = 512, 8, 8, 512
+    local_ids, recv_topk, psum = _build(
+        num_tokens, num_experts, top_k, 0.2, expert_start, seed=7
+    )
+    out = _run(recv_topk, psum, hidden, torch.float8_e4m3fn, expert_start)
+    _check(out, local_ids, psum)
+
+
+def test_ep_scatter_from_psum_drops_non_local_experts():
+    num_tokens, num_experts, top_k, hidden = 256, 8, 8, 512
+    expert_start = 8
+    local_ids, recv_topk, psum = _build(
+        num_tokens, num_experts, top_k, 0.0, expert_start, seed=11
+    )
+    # Send half of slot 0 to an expert this rank does not own; it must be treated
+    # exactly like padding, not scattered somewhere out of bounds.
+    foreign = torch.arange(num_tokens, device=dev) % 2 == 0
+    recv_topk[foreign, 0] = expert_start + num_experts + 3
+    dropped = local_ids[foreign, 0].clone()
+    local_ids[foreign, 0] = -1
+    counts = torch.bincount(dropped.long(), minlength=num_experts).to(psum.dtype)
+    psum = (
+        (torch.cat([psum[:1], psum[1:] - psum[:-1]]) - counts).cumsum(0).to(psum.dtype)
+    )
+
+    out = _run(recv_topk, psum, hidden, torch.float8_e4m3fn, expert_start)
+    _check(out, local_ids, psum)
+
+
+if __name__ == "__main__":
+    import sys
+
+    sys.exit(pytest.main([__file__, "-v", "-s"]))