An internal combustion engine in an engine exhaust passage of which a hydrocarbon feed valve and an exhaust purification catalyst are arranged. On the exhaust purification catalyst, platinum Pt is carried and a basic layer is formed. A concentration of hydrocarbons flowing into the exhaust purification catalyst is made to vibrate within a predetermined range of amplitude of 200 ppm or more and within a predetermined range of period of 5 seconds or less whereby NOx which is contained in the exhaust gas is reduced in the exhaust purification catalyst.