Exhaust purification system of internal combustion engine

An exhaust purification system of an internal combustion engine wherein a hydrocarbon feed valve for feeding hydrocarbons is arranged inside of an engine exhaust passage, an exhaust purification catalyst for reacting NOx contained in exhaust gas and hydrocarbons which are injected from the hydrocarbon feed valve and are partially oxidized is arranged in the engine exhaust passage downstream of the hydrocarbon feed valve, a precious metal catalyst is carried on the exhaust purification catalyst and a basic layer is formed on the exhaust purification catalyst, the exhaust purification catalyst has a property of reducing the NOx which is contained in the exhaust gas when hydrocarbons are injected from the hydrocarbon feed valve at predetermined feed intervals while maintaining an air-fuel ratio of an exhaust gas flowing into the exhaust purification catalyst lean and has a property of being increased in storage amount of NOx which is contained in the exhaust gas when the feed intervals of the hydrocarbons are longer than the predetermined feed intervals, and, at the time of engine operation, hydrocarbons are injected from the hydrocarbon feed valve at said predetermined feed intervals while maintaining the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst lean, and thereby NOx which is contained in exhaust gas is reduced at the exhaust purification catalyst.