diff --git a/mlir/include/mlir/Dialect/Math/IR/MathOps.td b/mlir/include/mlir/Dialect/Math/IR/MathOps.td
--- a/mlir/include/mlir/Dialect/Math/IR/MathOps.td
+++ b/mlir/include/mlir/Dialect/Math/IR/MathOps.td
@@ -226,6 +226,7 @@
     %a = math.cos %b : f64
     ```
   }];
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
diff --git a/mlir/lib/Dialect/Math/IR/MathOps.cpp b/mlir/lib/Dialect/Math/IR/MathOps.cpp
--- a/mlir/lib/Dialect/Math/IR/MathOps.cpp
+++ b/mlir/lib/Dialect/Math/IR/MathOps.cpp
@@ -97,6 +97,24 @@
                                       });
 }
 
+//===----------------------------------------------------------------------===//
+// CosOp folder
+//===----------------------------------------------------------------------===//
+
+OpFoldResult math::CosOp::fold(ArrayRef<Attribute> operands) {
+  return constFoldUnaryOpConditional<FloatAttr>(
+      operands, [](const APFloat &a) -> Optional<APFloat> {
+        switch (a.getSizeInBits(a.getSemantics())) {
+        case 64:
+          return APFloat(cos(a.convertToDouble()));
+        case 32:
+          return APFloat(cosf(a.convertToFloat()));
+        default:
+          return {};
+        }
+      });
+}
+
 //===----------------------------------------------------------------------===//
 // CountLeadingZerosOp folder
 //===----------------------------------------------------------------------===//
diff --git a/mlir/test/Dialect/Math/canonicalize.mlir b/mlir/test/Dialect/Math/canonicalize.mlir
--- a/mlir/test/Dialect/Math/canonicalize.mlir
+++ b/mlir/test/Dialect/Math/canonicalize.mlir
@@ -358,3 +358,20 @@
   return %0 : vector<4xf32>
 }
 
+// CHECK-LABEL: @cos_fold
+// CHECK-NEXT: %[[cst:.+]] = arith.constant 0.540302277 : f32
+// CHECK-NEXT:   return %[[cst]]
+func.func @cos_fold() -> f32 {
+  %c = arith.constant 1.0 : f32
+  %r = math.cos %c : f32
+  return %r : f32
+}
+
+// CHECK-LABEL: @cos_fold_vec
+// CHECK-NEXT: %[[cst:.+]] = arith.constant dense<[1.000000e+00, 0.540302277, 1.000000e+00, 0.540302277]> : vector<4xf32>
+// CHECK-NEXT:   return %[[cst]]
+func.func @cos_fold_vec() -> (vector<4xf32>) {
+  %v1 = arith.constant dense<[0.0, 1.0, 0.0, 1.0]> : vector<4xf32>
+  %0 = math.cos %v1 : vector<4xf32>
+  return %0 : vector<4xf32>
+}
diff --git a/mlir/test/mlir-cpu-runner/math-polynomial-approx.mlir b/mlir/test/mlir-cpu-runner/math-polynomial-approx.mlir
--- a/mlir/test/mlir-cpu-runner/math-polynomial-approx.mlir
+++ b/mlir/test/mlir-cpu-runner/math-polynomial-approx.mlir
@@ -357,7 +357,7 @@
   %cos_pi_over_4 = math.cos %pi_over_4 : f32
   vector.print %cos_pi_over_4 : f32
 
-  //// CHECK: 0
+  //// CHECK: -4.37114e-08
   %pi_over_2 = arith.constant 1.57079632679 : f32
   %cos_pi_over_2 = math.cos %pi_over_2 : f32
   vector.print %cos_pi_over_2 : f32
@@ -367,12 +367,12 @@
   %cos_pi = math.cos %pi : f32
   vector.print %cos_pi : f32
 
-  // CHECK: 0
-  %pi_3_over_2 = arith.constant 4.71238898038 : f32
+  // CHECK: 1.19249e-08
+  %pi_3_over_2 = arith.constant -4.71238898038 : f32
   %cos_pi_3_over_2 = math.cos %pi_3_over_2 : f32
   vector.print %cos_pi_3_over_2 : f32
 
-  // CHECK: -1, -0.5, 0
+  // CHECK: -1, -0.5, -4.37114e-08
   %vec_x = arith.constant dense<[9.42477796077, 2.09439510239, -1.57079632679]> : vector<3xf32>
   %cos_vec_x = math.cos %vec_x : vector<3xf32>
   vector.print %cos_vec_x : vector<3xf32>