In an internal combustion engine, a hydrocarbon feed valve and an exhaust purification catalyst are arranged in an engine exhaust passage. A first NOX removal method which reduces NOX contained in an exhaust gas by a reducing intermediate which is generated by injecting hydrocarbons from the hydrocarbon feed valve within a predetermined range of period and a second NOX removal method in which an air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is made rich by a period which is longer than this predetermined range are used. The switching temperatures ST and ST0 of the exhaust purification catalyst at which temperature an NOX removal method is switched from the second NOX removal method to the first NOX removal method, are made lower if the amount of NOX in the exhaust gas flowing into the exhaust purification catalyst increases.