diff --git a/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td b/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
--- a/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
+++ b/mlir/include/mlir/Dialect/Shape/IR/ShapeOps.td
@@ -179,6 +179,8 @@
   let results = (outs Shape_SizeType:$rank);
 
   let assemblyFormat = "attr-dict $shape";
+
+  let hasFolder = 1;
 }
 
 def Shape_ToExtentTensorOp : Shape_Op<"to_extent_tensor", [NoSideEffect]> {
diff --git a/mlir/lib/Dialect/Shape/IR/Shape.cpp b/mlir/lib/Dialect/Shape/IR/Shape.cpp
--- a/mlir/lib/Dialect/Shape/IR/Shape.cpp
+++ b/mlir/lib/Dialect/Shape/IR/Shape.cpp
@@ -437,6 +437,19 @@
   build(builder, result, shape, dimValue);
 }
 
+//===----------------------------------------------------------------------===//
+// RankOp
+//===----------------------------------------------------------------------===//
+
+OpFoldResult RankOp::fold(ArrayRef<Attribute> operands) {
+  auto shape = operands[0].dyn_cast_or_null<DenseIntElementsAttr>();
+  if (!shape)
+    return {};
+  int64_t rank = shape.getNumElements();
+  Builder builder(getContext());
+  return builder.getIndexAttr(rank);
+}
+
 //===----------------------------------------------------------------------===//
 // NumElementsOp
 //===----------------------------------------------------------------------===//
diff --git a/mlir/test/Dialect/Shape/canonicalize.mlir b/mlir/test/Dialect/Shape/canonicalize.mlir
--- a/mlir/test/Dialect/Shape/canonicalize.mlir
+++ b/mlir/test/Dialect/Shape/canonicalize.mlir
@@ -442,3 +442,27 @@
   "consume.witness"(%0) : (!shape.witness) -> ()
   return
 }
+
+// -----
+
+// Fold `rank` based on constant shape.
+// CHECK-LABEL: @fold_rank
+func @fold_rank() -> !shape.size {
+  // CHECK-DAG: %[[RESULT:.*]] = shape.const_size 5
+  // CHECK-DAG: return %[[RESULT]] : !shape.size
+  %shape = shape.const_shape [3, 4, 5, 6, 7]
+  %rank = shape.rank %shape
+  return %rank : !shape.size
+}
+
+// -----
+
+// Do not fold `rank` if shape is dynamic.
+// CHECK-LABEL: @dont_fold_rank
+// CHECK-SAME: (%[[SHAPE:.*]]: !shape.shape) -> !shape.size
+func @dont_fold_rank(%shape : !shape.shape) -> !shape.size {
+  // CHECK-DAG: %[[RESULT:.*]] = shape.rank %[[SHAPE]]
+  // CHECK-DAG: return %[[RESULT]] : !shape.size
+  %rank = shape.rank %shape
+  return %rank : !shape.size
+}