An exhaust purification system for an internal combustion engine which has a plurality of cylinders, said exhaust purification system comprising: an exhaust purification catalyst configured to be arranged in an engine exhaust passage and capable of storing oxygen; a downstream side air-fuel ratio sensor which is arranged at a downstream side of the exhaust purification catalyst in a direction of flow of exhaust; and a control device for controlling combustion air-fuel ratios when combustion is performed in the cylinders, wherein the control device is configured to: perform average air-fuel ratio control which controls an average air-fuel ratio of an average of the combustion air-fuel ratios of all cylinders alternately between a rich air-fuel ratio which is richer than a stoichiometric air-fuel ratio and a lean air-fuel ratio which is leaner than the stoichiometric air-fuel ratio, based on the air-fuel ratio (AFdwn) outputted by the downstream side air-fuel ratio sensor; and perform inter-cylinder air-fuel ratio control which controls the combustion air-fuel ratios of the cylinders so that the combustion air-fuel ratio comes to match the rich air-fuel ratio at least at one cylinder among the plurality of cylinders even if the average air-fuel ratio is controlled to the lean air-fuel ratio by the average air-fuel ratio control; and control the average air-fuel ratio in the average air-fuel ratio control so that a lean shift amount which is a difference between the average air-fuel ratio and stoichiometric air-fuel ratio when controlling the average air-fuel ratio to a lean air-fuel ratio becomes smaller than a rich shift amount which is a difference between the average air-fuel ratio and stoichiometric air-fuel ratio when controlling the average air-fuel ratio to a rich air-fuel ratio. an exhaust purification catalyst configured to be arranged in an engine exhaust passage and capable of storing oxygen; a downstream side air-fuel ratio sensor which is arranged at a downstream side of the exhaust purification catalyst in a direction of flow of exhaust; and a control device for controlling combustion air-fuel ratios when combustion is performed in the cylinders, wherein the control device is configured to: perform average air-fuel ratio control which controls an average air-fuel ratio of an average of the combustion air-fuel ratios of all cylinders alternately between a rich air-fuel ratio which is richer than a stoichiometric air-fuel ratio and a lean air-fuel ratio which is leaner than the stoichiometric air-fuel ratio, based on the air-fuel ratio (AFdwn) outputted by the downstream side air-fuel ratio sensor; and perform inter-cylinder air-fuel ratio control which controls the combustion air-fuel ratios of the cylinders so that the combustion air-fuel ratio comes to match the rich air-fuel ratio at least at one cylinder among the plurality of cylinders even if the average air-fuel ratio is controlled to the lean air-fuel ratio by the average air-fuel ratio control; and control the average air-fuel ratio in the average air-fuel ratio control so that a lean shift amount which is a difference between the average air-fuel ratio and stoichiometric air-fuel ratio when controlling the average air-fuel ratio to a lean air-fuel ratio becomes smaller than a rich shift amount which is a difference between the average air-fuel ratio and stoichiometric air-fuel ratio when controlling the average air-fuel ratio to a rich air-fuel ratio. perform average air-fuel ratio control which controls an average air-fuel ratio of an average of the combustion air-fuel ratios of all cylinders alternately between a rich air-fuel ratio which is richer than a stoichiometric air-fuel ratio and a lean air-fuel ratio which is leaner than the stoichiometric air-fuel ratio, based on the air-fuel ratio (AFdwn) outputted by the downstream side air-fuel ratio sensor; and perform inter-cylinder air-fuel ratio control which controls the combustion air-fuel ratios of the cylinders so that the combustion air-fuel ratio comes to match the rich air-fuel ratio at least at one cylinder among the plurality of cylinders even if the average air-fuel ratio is controlled to the lean air-fuel ratio by the average air-fuel ratio control; and control the average air-fuel ratio in the average air-fuel ratio control so that a lean shift amount which is a difference between the average air-fuel ratio and stoichiometric air-fuel ratio when controlling the average air-fuel ratio to a lean air-fuel ratio becomes smaller than a rich shift amount which is a difference between the average air-fuel ratio and stoichiometric air-fuel ratio when controlling the average air-fuel ratio to a rich air-fuel ratio.