An internal combustion engine in which a hydrocarbon feed valve, exhaust purification catalyst, and NOX selective reduction catalyst are arranged in an engine exhaust passage. A first NOX removal method which injects hydrocarbons from the hydrocarbon feed valve within a predetermined range of period and uses the reducing intermediate which is generated due to this so as to reduce the NOX contained in the exhaust gas and a second NOX removal method which makes the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst rich with a period longer than this predetermined range are used. When the first NOX removal method should be used and the amount of adsorbed ammonia at the NOX selective reduction catalyst is large, use of the first NOX removal method is stopped.