Abstract: An off-road vehicle includes a frame and an engine. The engine includes a cylinder block and a cylinder head, on which an exhaust passage is arranged. The cylinder head is provided with a supplementary air supply passage for mixing air into the exhaust gas discharged from the combustion chamber. Alternatively, the supplementary air supply passage can be included in the exhaust system, such as in a cylinder head mounting flange of the exhaust pipe, upstream of an oxygen sensor and first and second stage catalytic converters. The exhaust gas from the engine is further oxidized by air, which reduces the content of components such as CO and NOx in the exhaust gas, improving environmental protection.