diff --git a/crates/uv-requirements/src/sources.rs b/crates/uv-requirements/src/sources.rs
index 92aa97b42586d..0f5f07be77367 100644
--- a/crates/uv-requirements/src/sources.rs
+++ b/crates/uv-requirements/src/sources.rs
@@ -23,6 +23,8 @@ pub enum RequirementsSource {
     SetupCfg(PathBuf),
     /// Dependencies were provided via a path to a source tree (e.g., `pip install .`).
     SourceTree(PathBuf),
+    /// Dependencies were provided via an unsupported Conda `environment.yml` file (e.g., `pip install -r environment.yml`).
+    EnvironmentYml(PathBuf),
 }
 
 impl RequirementsSource {
@@ -35,6 +37,8 @@ impl RequirementsSource {
             Self::SetupPy(path)
         } else if path.ends_with("setup.cfg") {
             Self::SetupCfg(path)
+        } else if path.ends_with("environment.yml") {
+            Self::EnvironmentYml(path)
         } else {
             Self::RequirementsTxt(path)
         }
@@ -217,6 +221,7 @@ impl std::fmt::Display for RequirementsSource {
             | Self::PyprojectToml(path)
             | Self::SetupPy(path)
             | Self::SetupCfg(path)
+            | Self::EnvironmentYml(path)
             | Self::SourceTree(path) => {
                 write!(f, "{}", path.simplified_display())
             }
diff --git a/crates/uv-requirements/src/specification.rs b/crates/uv-requirements/src/specification.rs
index 32b9ef2085366..0f16ada104ccc 100644
--- a/crates/uv-requirements/src/specification.rs
+++ b/crates/uv-requirements/src/specification.rs
@@ -212,6 +212,12 @@ impl RequirementsSpecification {
                     ..Self::default()
                 }
             }
+            RequirementsSource::EnvironmentYml(path) => {
+                return Err(anyhow::anyhow!(
+                    "Conda environment files (i.e. `{}`) are not supported",
+                    path.user_display()
+                ))
+            }
         })
     }
 
diff --git a/crates/uv/tests/it/edit.rs b/crates/uv/tests/it/edit.rs
index 4f8b6cccd89c0..013b2725d61e0 100644
--- a/crates/uv/tests/it/edit.rs
+++ b/crates/uv/tests/it/edit.rs
@@ -3662,6 +3662,41 @@ fn add_error() -> Result<()> {
     Ok(())
 }
 
+/// Emit dedicated error message when adding Conda `environment.yml`
+#[test]
+fn add_environment_yml_error() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = []
+    "#})?;
+
+    let environment_yml = context.temp_dir.child("environment.yml");
+    environment_yml.write_str(indoc! {r"
+        name: test-env
+        channels:
+          - conda-forge
+        dependencies:
+          - python>=3.12
+    "})?;
+
+    uv_snapshot!(context.filters(), context.add().arg("-r").arg("environment.yml"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Conda environment files (i.e. `environment.yml`) are not supported
+    ");
+
+    Ok(())
+}
+
 /// Set a lower bound when adding unconstrained dependencies.
 #[test]
 fn add_lower_bound() -> Result<()> {
diff --git a/crates/uv/tests/it/pip_install.rs b/crates/uv/tests/it/pip_install.rs
index 12e2a4cc0af14..93b64236e7429 100644
--- a/crates/uv/tests/it/pip_install.rs
+++ b/crates/uv/tests/it/pip_install.rs
@@ -8028,6 +8028,32 @@ fn install_incompatible_python_version_interpreter_broken_in_path() -> Result<()
     Ok(())
 }
 
+/// Emit dedicated error message when installing Conda `environment.yml`
+#[test]
+fn install_unsupported_environment_yml() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let environment_yml = context.temp_dir.child("environment.yml");
+    environment_yml.write_str(indoc! {r"
+        name: test-env
+        channels:
+          - conda-forge
+        dependencies:
+          - python>=3.12
+    "})?;
+
+    uv_snapshot!(context.filters(), context.pip_install().arg("-r").arg("environment.yml"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Conda environment files (i.e. `environment.yml`) are not supported
+    ");
+
+    Ok(())
+}
+
 /// Include a `build_constraints.txt` file with an incompatible constraint.
 #[test]
 fn incompatible_build_constraint() -> Result<()> {