An exhaust purification system for an internal combustion engine in which a hydrocarbon feed valve for feeding hydrocarbons is arranged inside of an engine exhaust passage, an exhaust purification catalyst for reacting NO x contained in exhaust gas and reformed hydrocarbons is arranged inside of the engine exhaust passage downstream of the hydrocarbon feed valve, a precious metal catalyst (51, 52) is carried on an exhaust gas flow surface of the exhaust purification catalyst, a basic exhaust gas flow surface part is formed around the precious metal catalysts (51, 52), the exhaust purification catalyst has a property of reducing the NO x which is contained in exhaust gas if a concentration of hydrocarbons flowing into the exhaust purification catalyst is made to vibrate within a predetermined range of amplitude and within a predetermined range of period and has a property of being increased in storage amount of NO x which is contained in exhaust gas if the vibration period of the hydrocarbon concentration is made longer than the predetermined range, at the time of engine operation, the exhaust purification system further comprises: control means adapted so that the injection amount of hydrocarbons from the hydrocarbon feed valve is controlled so that the amplitude of the change of concentration of hydrocarbons flowing into the exhaust purification catalyst becomes within said predetermined range of amplitude, and the injection period of hydrocarbons from the hydrocarbon feed valve is controlled so that the concentration of hydrocarbons flowing into the exhaust purification catalyst vibrates by said predetermined range of period, wherein an NO 2 reduction catalyst which is able to reduce NO 2 which is contained in exhaust gas to NO when hydrocarbons are fed is arranged inside of the engine exhaust passage downstream of the exhaust purification catalyst, and the control means is further adapted so that, when the NO 2 which is contained in the exhaust gas should be reduced to NO, the amplitude of change of the concentration of hydrocarbons flowing into the exhaust purification catalyst is increased to increase a pass through amount of hydrocarbons which pass straight through the exhaust purification catalyst, wherein a particulate filter is arranged inside of the engine exhaust passage between said exhaust purification catalyst and said NO 2 reduction catalyst, said particulate filter has an NO 2 producing ability, and the control means is further adapted so that a pass through amount of hydrocarbons which pass straight through the exhaust purification catalyst is made to increase when the NO 2 which is produced on the particulate filter should be reduced to NO. control means adapted so that the injection amount of hydrocarbons from the hydrocarbon feed valve is controlled so that the amplitude of the change of concentration of hydrocarbons flowing into the exhaust purification catalyst becomes within said predetermined range of amplitude, and the injection period of hydrocarbons from the hydrocarbon feed valve is controlled so that the concentration of hydrocarbons flowing into the exhaust purification catalyst vibrates by said predetermined range of period,