diff --git a/flang/include/flang/Optimizer/HLFIR/HLFIROps.td b/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
index fdf0db9d3c75d..b162af55d66bb 100644
--- a/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
+++ b/flang/include/flang/Optimizer/HLFIR/HLFIROps.td
@@ -130,7 +130,7 @@ def hlfir_DeclareOp : hlfir_Op<"declare", [AttrSizedOperandSegments,
   let hasVerifier = 1;
 }
 
-def fir_AssignOp : hlfir_Op<"assign", [MemoryEffects<[MemWrite]>]> {
+def fir_AssignOp : hlfir_Op<"assign", [DeclareOpInterfaceMethods<MemoryEffectsOpInterface>]> {
   let summary = "Assign an expression or variable value to a Fortran variable";
 
   let description = [{
@@ -166,7 +166,7 @@ def fir_AssignOp : hlfir_Op<"assign", [MemoryEffects<[MemWrite]>]> {
   }];
 
   let arguments = (ins AnyFortranEntity:$rhs,
-                   Arg<AnyFortranVariable, "", [MemWrite]>:$lhs,
+                   AnyFortranVariable:$lhs,
                    UnitAttr:$realloc,
                    UnitAttr:$keep_lhs_length_if_realloc,
                    UnitAttr:$temporary_lhs);
diff --git a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
index ed301c74c9ede..b593383ff2848 100644
--- a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
+++ b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
@@ -90,6 +90,62 @@ llvm::LogicalResult hlfir::AssignOp::verify() {
   return mlir::success();
 }
 
+void hlfir::AssignOp::getEffects(
+    llvm::SmallVectorImpl<
+        mlir::SideEffects::EffectInstance<mlir::MemoryEffects::Effect>>
+        &effects) {
+  mlir::OpOperand &rhs = getRhsMutable();
+  mlir::OpOperand &lhs = getLhsMutable();
+  mlir::Type rhsType = getRhs().getType();
+  mlir::Type lhsType = getLhs().getType();
+  if (mlir::isa<fir::RecordType>(hlfir::getFortranElementType(lhsType))) {
+    // For derived type assignments, set unknown read/write effects since it
+    // is not known here if user defined finalization is needed, and also
+    // because allocatable components may lead to "deeper" read/write effects
+    // that cannot be described with this API.
+    effects.emplace_back(mlir::MemoryEffects::Read::get(),
+                         mlir::SideEffects::DefaultResource::get());
+    effects.emplace_back(mlir::MemoryEffects::Write::get(),
+                         mlir::SideEffects::DefaultResource::get());
+  } else {
+    // Read effect when RHS is a variable.
+    if (hlfir::isFortranVariableType(rhsType)) {
+      if (hlfir::isBoxAddressType(rhsType)) {
+        // Unknown read effect if the RHS is a descriptor since the read effect
+        // on the data cannot be described.
+        effects.emplace_back(mlir::MemoryEffects::Read::get(),
+                             mlir::SideEffects::DefaultResource::get());
+      } else {
+        effects.emplace_back(mlir::MemoryEffects::Read::get(), &rhs,
+                             mlir::SideEffects::DefaultResource::get());
+      }
+    }
+
+    // Write effects on LHS.
+    if (hlfir::isBoxAddressType(lhsType)) {
+      //  If the LHS is a descriptor, the descriptor will be read and the data
+      //  write cannot be described in this API (and the descriptor may be
+      //  written to in case of realloc, which is covered by the unknown write
+      //  effect.
+      effects.emplace_back(mlir::MemoryEffects::Read::get(), &lhs,
+                           mlir::SideEffects::DefaultResource::get());
+      effects.emplace_back(mlir::MemoryEffects::Write::get(),
+                           mlir::SideEffects::DefaultResource::get());
+    } else {
+      effects.emplace_back(mlir::MemoryEffects::Write::get(), &lhs,
+                           mlir::SideEffects::DefaultResource::get());
+    }
+  }
+
+  if (getRealloc()) {
+    // Reallocation of the data cannot be precisely described by this API.
+    effects.emplace_back(mlir::MemoryEffects::Free::get(),
+                         mlir::SideEffects::DefaultResource::get());
+    effects.emplace_back(mlir::MemoryEffects::Allocate::get(),
+                         mlir::SideEffects::DefaultResource::get());
+  }
+}
+
 //===----------------------------------------------------------------------===//
 // DeclareOp
 //===----------------------------------------------------------------------===//
diff --git a/flang/test/HLFIR/assign-side-effects.fir b/flang/test/HLFIR/assign-side-effects.fir
new file mode 100644
index 0000000000000..dfd1c5886e4fa
--- /dev/null
+++ b/flang/test/HLFIR/assign-side-effects.fir
@@ -0,0 +1,31 @@
+// Test side effects of hlfir.assign op.
+// RUN: fir-opt %s --test-side-effects --verify-diagnostics
+
+func.func @test1(%x: !fir.ref<i32>, %i: i32) {
+  // expected-remark @below {{found an instance of 'write' on a op operand, on resource '<Default>'}}
+  hlfir.assign %i to %x : i32, !fir.ref<i32>
+  return
+}
+
+func.func @test2(%x: !fir.ref<i32>, %y: !fir.ref<i32>) {
+  // expected-remark @below {{found an instance of 'write' on a op operand, on resource '<Default>'}}
+  // expected-remark @below {{found an instance of 'read' on a op operand, on resource '<Default>'}}
+  hlfir.assign %y to %x : !fir.ref<i32>, !fir.ref<i32>
+  return
+}
+
+func.func @test3(%x: !fir.ref<!fir.type<t>>, %y: !fir.ref<!fir.type<t>>) {
+  // expected-remark @below {{found an instance of 'write' on resource '<Default>'}}
+  // expected-remark @below {{found an instance of 'read' on resource '<Default>'}}
+  hlfir.assign %y to %x : !fir.ref<!fir.type<t>>, !fir.ref<!fir.type<t>>
+  return
+}
+
+func.func @test4(%x: !fir.ref<!fir.box<!fir.heap<!fir.array<?xi32>>>>, %y: !fir.box<!fir.array<?xi32>>) {
+  // expected-remark @below {{found an instance of 'read' on a op operand, on resource '<Default>'}}
+  // expected-remark @below {{found an instance of 'write' on resource '<Default>'}}
+  // expected-remark @below {{found an instance of 'free' on resource '<Default>'}}
+  // expected-remark @below {{found an instance of 'allocate' on resource '<Default>'}}
+  hlfir.assign %y to %x realloc : !fir.box<!fir.array<?xi32>>, !fir.ref<!fir.box<!fir.heap<!fir.array<?xi32>>>>
+  return
+}