A control system of an internal combustion engine comprising an exhaust purification catalyst arranged in an exhaust passage of the internal combustion engine and able to store oxygen, and a downstream side air-fuel ratio sensor arranged at a downstream side of the exhaust purification catalyst in a direction of exhaust flow and detecting an air-fuel ratio of exhaust gas flowing out from the exhaust purification catalyst, wherein the control system performs feedback control of an amount of fuel fed to a combustion chamber of the internal combustion engine so that an air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst becomes a target air-fuel ratio and performs learning control, the target air-fuel ratio is switched to the lean set air-fuel ratio when an air-fuel ratio detected by the downstream side air-fuel ratio sensor becomes a rich judged air-fuel ratio, which is richer than a stoichiometric air-fuel ratio, or less, and is switched to the rich set air-fuel ratio when an oxygen storage amount of the exhaust purification catalyst becomes a predetermined switching reference storage amount (Cref), smaller than a maximum storable oxygen amount (Cmax), or more, or when an air-fuel ratio detected by the downstream side air-fuel ratio sensor becomes a lean judged air-fuel ratio, which is leaner than a stoichiometric air-fuel ratio, or more, in the learning control, based on a first oxygen cumulative value which is an absolute value of a cumulative oxygen excess/deficiency (∑ODE) in a first time period from when switching the target air-fuel ratio to the lean set air-fuel ratio to when the oxygen storage amount of the exhaust purification catalyst becomes the switching reference amount (Cref) or more, or to when an air-fuel ratio detected by the downstream side air-fuel ratio sensor becomes the lean judged air-fuel ratio, and a second oxygen cumulative value which is an absolute value of a cumulative oxygen excess/deficiency (∑ODE) in a second time period from when switching the target air-fuel ratio to the rich set air-fuel ratio to when an air-fuel ratio detected by the downstream side air-fuel ratio sensor becomes the rich judged air-fuel ratio or less, a parameter relating to an air-fuel ratio is corrected so that a difference between these first oxygen cumulative value and second oxygen cumulative value becomes smaller, and when a condition for learning acceleration, which is satisfied when it is necessary to accelerate correction of the parameter by the learning control, is satisfied, a rich degree of the rich set air-fuel ratio is increased. the control system performs feedback control of an amount of fuel fed to a combustion chamber of the internal combustion engine so that an air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst becomes a target air-fuel ratio and performs learning control, the target air-fuel ratio is switched to the lean set air-fuel ratio when an air-fuel ratio detected by the downstream side air-fuel ratio sensor becomes a rich judged air-fuel ratio, which is richer than a stoichiometric air-fuel ratio, or less, and is switched to the rich set air-fuel ratio when an oxygen storage amount of the exhaust purification catalyst becomes a predetermined switching reference storage amount (Cref), smaller than a maximum storable oxygen amount (Cmax), or more, or when an air-fuel ratio detected by the downstream side air-fuel ratio sensor becomes a lean judged air-fuel ratio, which is leaner than a stoichiometric air-fuel ratio, or more, is switched to the lean set air-fuel ratio when an air-fuel ratio detected by the downstream side air-fuel ratio sensor becomes a rich judged air-fuel ratio, which is richer than a stoichiometric air-fuel ratio, or less, and is switched to the rich set air-fuel ratio when an oxygen storage amount of the exhaust purification catalyst becomes a predetermined switching reference storage amount (Cref), smaller than a maximum storable oxygen amount (Cmax), or more, or when an air-fuel ratio detected by the downstream side air-fuel ratio sensor becomes a lean judged air-fuel ratio, which is leaner than a stoichiometric air-fuel ratio, or more, in the learning control, based on a first oxygen cumulative value which is an absolute value of a cumulative oxygen excess/deficiency (∑ODE) in a first time period from when switching the target air-fuel ratio to the lean set air-fuel ratio to when the oxygen storage amount of the exhaust purification catalyst becomes the switching reference amount (Cref) or more, or to when an air-fuel ratio detected by the downstream side air-fuel ratio sensor becomes the lean judged air-fuel ratio, and a second oxygen cumulative value which is an absolute value of a cumulative oxygen excess/deficiency (∑ODE) in a second time period from when switching the target air-fuel ratio to the rich set air-fuel ratio to when an air-fuel ratio detected by the downstream side air-fuel ratio sensor becomes the rich judged air-fuel ratio or less, a parameter relating to an air-fuel ratio is corrected so that a difference between these first oxygen cumulative value and second oxygen cumulative value becomes smaller, and when a condition for learning acceleration, which is satisfied when it is necessary to accelerate correction of the parameter by the learning control, is satisfied, a rich degree of the rich set air-fuel ratio is increased.