Route 21A, or Highway 21A, may refer to:
India National Highway 21A (India)
United States County Road 21A (Clay County, Florida) M-21A (Michigan highway) (former) Nebraska Spur 21A New Jersey Route 21A (former) New York State Route 21A (former) County Route 21A (Suffolk County, New York) County Route 21A (Sullivan County, New York) County Route 21A (Warren County, New York) Secondary State Highway 21A (Washington) (former)
See also List of A21 roads