A cooking appliance includes a frame defining a cooking chamber, a a magnetron for generating microwaves to cook food received in the cooking chamber, a door connected to the frame and configured to open and close the cooking chamber, a gasket disposed at the door and configured to contact a front portion of the frame based on the door closing the cooking chamber, and a leakage prevention part that is disposed at the door and that defines a space portion for preventing leakage of the microwaves. The gasket is coupled to the space portion.