The invention discloses a rotary internal combustion engine that includes a cylinder with circular section, containing two identical cylinder blocks with semi-circular sections. Two identical rotors are installed within the cylinder block and are provided with four pistons with piston rings similar to the reciprocation engine. Two identical rotor shafts are vertically fixed on the two rotors respectively. Two non-circular gears are installed on the two rotor shafts separately, which engage with two eccentric gears respectively attached to one output shaft respectively. The rotors work four times every revolution, equivalent to the work done by a 4 cylinder 4 stroke internal combustion engine for every two revolutions of the crankshaft. The engine may include multi spark plugs or injectors, multi intake ports and multi exhaust ports. The engine may also combine multi cylinder blocks to provide larger output power.