The invention relates to the field of power machinery, in particular to an internal combustion engine with rotor pistons. The internal combustion engine is characterized in that 1, the two pistons which are mounted oppositely intermittently rotate around a center shaft in a cylindrical cylinder, air suction, compression, explosion and exhaust stoke are completed, energy of exploded gas acts on side surfaces of the pistons, output shafts are directly pushed to rotate, and the problem of energy dissipation of an engine with a reciprocating piston due to change of an included angle between a crank and a connecting rod is avoided; 2, compared with an engine with a reciprocating piston and a triangular rotor, the internal combustion engine does not have a reciprocating part or a movable valve or components thereof, does not realize eccentric movement, accordingly does not cause structural vibration, and is low in self consumption; 3, compared with a triangular rotor engine adopting a linear sealing component, the engine realizes surface sealing, does not need parts such as sealing strips and the like which are difficult in processing and easy to be worn, and is fine in sealing performance and high in reliability; 4, abrasion rate is low, abrasion of a main portion only depends on the abrasion degree of a bearing; and 5, the total engine is simple and compact in structure and high in thermal efficiency.