The exhaust purification system comprises an exhaust purification catalyst 20, a downstream side air-fuel ratio sensor 41, and a control device 31. The control device 31 performs average air-fuel ratio control which alternatively sets a target average air-fuel ratio between a rich air-fuel ratio and a lean air-fuel ratio and inter-cylinder air-fuel ratio control which controls the target air-fuel ratios of the cylinders so that the target air-fuel ratio becomes the rich air-fuel ratio at least at one cylinder among the plurality of cylinders even if the target average air-fuel ratio is set to the lean air-fuel ratio. As learning control, the control device 31 uses a cumulative value of a first oxygen amount from a time when the target average air-fuel ratio to the lean air-fuel ratio to a time when the target average air-fuel ratio is switched back to the rich air-fuel ratio and a cumulative value of a second oxygen amount from a time when the target average air-fuel ratio is switched to the rich air-fuel ratio to when again switching it to the lean air-fuel ratio as the basis for correcting a parameter relating to the air-fuel ratio so that the difference of these decreases.