Abstract: A Stator-Rotor piston internal combustion engine (50) is diclosed having two identical stator halves (5) with an equal number of cylinders in each of them, a flat rotor (6) with two internal gear rings (12) fitted on its periphery and two auxiliary gears (13) sliding on its hubs (14), the rotor (6) being fixed on the engine shaft (7) between both stator halves. Each cylinder is provided with own crankshaft (10) and a drive gear (11) mounted thereon. All drive gears (11) are engaged with the rotor internal gear rings (12) and the auxiliary gears (13) for transmitting the explosion power to the engine shaft (7). As a result of the transmission ratio between the drive gears (11) and the internal gear rings (12) the engine revolutions are reduced in comparison with those of the single crankshafts. For smooth running characteristics of the engine two opposite cylinders explode simultaneously, one of each stator half, and the firing order runs in a circle: 1+3A, 2+4A, 3+1A, 4+2A.