An exhaust gas purification system for a hydrogen engine is provided in which hydrogen gas is supplied in the hydrogen engine as a fuel for combustion, and is also supplied to the exhaust gas after combustion to improve purification of the exhaust element. The exhaust gas purification system includes a hydrogen storage tank, the hydrogen engine, and a catalyst provided in an exhaust pipe, and is capable of supplying hydrogen gas through the exhaust pipe during operation of the hydrogen engine. An upstream-side exhaust gas sensor is provided on the exhaust pipe upstream of the catalyst. An exhaust-side hydrogen gas injection device is provided upstream of the upstream-side exhaust gas sensor. Control means control the amount of hydrogen gas for supply to the hydrogen engine based on the detection by the upstream-side exhaust gas sensor as a feedback control so as to obtain the exhaust gas having a predetermined lean air-fuel ratio, and control the amount of hydrogen gas supplied from the exhaust-side hydrogen gas injection device to be less than that supplied to the hydrogen engine.