diff --git a/e2e-win/env_cache_venv.Tests.ps1 b/e2e-win/env_cache_venv.Tests.ps1
new file mode 100644
index 0000000000..6311ec5749
--- /dev/null
+++ b/e2e-win/env_cache_venv.Tests.ps1
@@ -0,0 +1,60 @@
+# Regression test for the Windows path of the env_cache / uv venv interaction.
+# See e2e/env/test_env_cache_venv for the full rationale: the env cache key did
+# not account for the uv.lock / .venv that python.uv_venv_auto discovers via
+# find_up, so a venv leaked across directories sharing the same config files.
+
+Describe 'env_cache uv venv' {
+    BeforeAll {
+        $script:OriginalDir = Get-Location
+
+        $env:MISE_EXPERIMENTAL = "1"
+        $env:MISE_ENV_CACHE = "1"
+        # Fixed encryption key, as `mise activate` would set.
+        $env:__MISE_ENV_CACHE_KEY = "dGVzdGtleXRlc3RrZXl0ZXN0a2V5dGVzdGtleXRlc3Q="
+
+        $script:TestRoot = Join-Path $TestDrive ([System.Guid]::NewGuid().ToString())
+        New-Item -ItemType Directory -Path $script:TestRoot | Out-Null
+        $env:MISE_STATE_DIR = Join-Path $script:TestRoot "state"
+
+        # venv auto-source lives in the parent config so both child dirs resolve
+        # the same config files (and thus the same cache key); neither child has
+        # its own config.
+        @"
+[settings]
+python.uv_venv_auto = "source"
+"@ | Out-File (Join-Path $script:TestRoot ".mise.toml")
+        $env:MISE_TRUSTED_CONFIG_PATHS = $script:TestRoot
+
+        # "source" mode only needs an existing .venv directory and a uv.lock, so
+        # no python/uv install is required.
+        $script:Proj = Join-Path $script:TestRoot "proj"
+        $script:Other = Join-Path $script:TestRoot "other"
+        New-Item -ItemType Directory -Force -Path (Join-Path $script:Proj ".venv\Scripts") | Out-Null
+        New-Item -ItemType Directory -Force -Path $script:Other | Out-Null
+        New-Item -ItemType File -Force -Path (Join-Path $script:Proj "uv.lock") | Out-Null
+    }
+
+    AfterAll {
+        Set-Location $script:OriginalDir
+        Remove-Item Env:MISE_EXPERIMENTAL, Env:MISE_ENV_CACHE, Env:__MISE_ENV_CACHE_KEY, `
+            Env:MISE_STATE_DIR, Env:MISE_TRUSTED_CONFIG_PATHS -ErrorAction Ignore
+    }
+
+    It 'does not leak the venv into a sibling without a uv.lock' {
+        Set-Location $script:Proj
+        (mise env | Out-String) | Should -Match "VIRTUAL_ENV"
+
+        Set-Location $script:Other
+        (mise env | Out-String) | Should -Not -Match "VIRTUAL_ENV"
+    }
+
+    It 'does not let a cached non-venv sibling suppress the venv' {
+        Remove-Item (Join-Path $env:MISE_STATE_DIR "env-cache") -Recurse -Force -ErrorAction Ignore
+
+        Set-Location $script:Other
+        (mise env | Out-String) | Should -Not -Match "VIRTUAL_ENV"
+
+        Set-Location $script:Proj
+        (mise env | Out-String) | Should -Match "VIRTUAL_ENV"
+    }
+}
diff --git a/e2e/env/test_env_cache_venv b/e2e/env/test_env_cache_venv
new file mode 100644
index 0000000000..f876d877f5
--- /dev/null
+++ b/e2e/env/test_env_cache_venv
@@ -0,0 +1,60 @@
+#!/usr/bin/env bash
+# Regression test: env_cache must not leak a uv venv across directories.
+#
+# The env cache key (compute_env_cache_key in src/toolset/toolset_env.rs) is
+# derived from the resolved config files (+ sibling mise.lock), tool versions,
+# settings and the base PATH. But NOT from the current directory or the
+# uv.lock / .venv location that `python.uv_venv_auto` discovers via find_up.
+#
+# As a result two directories that resolve the same config files share one
+# cache key, even though only one of them contains a uv venv. Whichever
+# directory computes its env first wins for both, so:
+#   * the venv "stays active" after leaving the project dir, and
+#   * a project venv can fail to activate if a non-venv sibling cached first.
+#
+# Both are the same root cause and both are exercised below. A correct fix
+# (making the cache key aware of cwd / uv.lock) satisfies both; a fix that
+# merely marks the venv directive uncacheable would still fail scenario 2.
+
+set -euo pipefail
+
+export MISE_EXPERIMENTAL=1
+# Enable env caching with a fixed encryption key, as `mise activate` would set.
+export MISE_ENV_CACHE=1
+export __MISE_ENV_CACHE_KEY="dGVzdGtleXRlc3RrZXl0ZXN0a2V5dGVzdGtleXRlc3Q="
+
+# uv venv auto-source lives in the GLOBAL config so that both directories below
+# resolve the exact same set of config files -> the same cache key. Neither
+# directory has a local mise.toml.
+cat >"$MISE_CONFIG_DIR/config.toml" <<EOF
+[settings]
+python.uv_venv_auto = "source"
+EOF
+
+# "source" mode only needs an existing .venv directory and a uv.lock; it does
+# not create anything, so no python/uv install is required for this test.
+mkdir -p proj/.venv/bin other
+: >proj/uv.lock
+
+# Sanity check: the venv activates inside the project directory.
+cd proj
+assert_contains "mise env -s bash" "VIRTUAL_ENV=$PWD/.venv"
+cd ..
+
+# Scenario 1 -- venv must not leak into a sibling without a uv.lock.
+# (Equivalent to "VIRTUAL_ENV stays set after leaving the venv directory".)
+# proj computed first and cached its env (with venv) under the shared key;
+# `other` then gets a cache hit and wrongly inherits VIRTUAL_ENV.
+cd other
+assert_not_contains "mise env -s bash" "VIRTUAL_ENV"
+cd ..
+
+# Scenario 2 -- a non-venv sibling must not suppress the project's venv.
+# Start from a clean cache, visit `other` first (caches a "no venv" env under
+# the shared key), then the project dir must STILL activate its venv.
+rm -rf "${MISE_STATE_DIR:?}/env-cache"
+cd other
+assert_not_contains "mise env -s bash" "VIRTUAL_ENV"
+cd ../proj
+assert_contains "mise env -s bash" "VIRTUAL_ENV=$PWD/.venv"
+cd ..
diff --git a/src/toolset/toolset_env.rs b/src/toolset/toolset_env.rs
index 9bc2fb93e9..5d0f581a8b 100644
--- a/src/toolset/toolset_env.rs
+++ b/src/toolset/toolset_env.rs
@@ -269,8 +269,23 @@ impl Toolset {
             .map(|p| p.to_string_lossy().to_string())
             .unwrap_or_default();
 
+        // Include the auto-sourced uv venv (uv.lock + .venv) in the key so a venv
+        // dir and a sibling sharing the same config files don't collide on one
+        // cache entry, which would leak the venv across directories.
+        let mut uv_venv_inputs: Vec<(PathBuf, u64)> = Vec::new();
+        if Settings::get().python.uv_venv_auto.should_source()
+            && let Some(uv_root) = uv::uv_root()
+        {
+            let lock = uv_root.join("uv.lock");
+            let venv = uv_root.join(".venv");
+            let lock_mtime = get_file_mtime(&lock).unwrap_or(0);
+            let venv_mtime = get_file_mtime(&venv).unwrap_or(0);
+            uv_venv_inputs.push((lock, lock_mtime));
+            uv_venv_inputs.push((venv, venv_mtime));
+        }
+
         Ok(CachedEnv::compute_cache_key(
-            &[config_files, config_lockfiles].concat(),
+            &[config_files, config_lockfiles, uv_venv_inputs].concat(),
             &tool_versions,
             &settings_hash,
             &base_path,
diff --git a/src/uv.rs b/src/uv.rs
index 780edc861a..f9ef573669 100644
--- a/src/uv.rs
+++ b/src/uv.rs
@@ -74,7 +74,7 @@ pub async fn uv_venv(config: &Arc<Config>, ts: &Toolset) -> &'static Option<Venv
         .await
 }
 
-fn uv_root() -> Option<PathBuf> {
+pub(crate) fn uv_root() -> Option<PathBuf> {
     file::find_up(dirs::CWD.as_ref()?, &["uv.lock"]).map(|p| p.parent().unwrap().to_path_buf())
 }