A combustion controller for a two-cycle engine which enables to cause self firing always at the optimum timing is provided. The combustion controller comprises an exhaust control valve 15 provided in the vicinity of an exhaust port 7 of the two-cycle engine 1 and capable of fully closing the exhaust port and driving control means 47, 38, 39, 40 and 37 to drive the exhaust control valve 15 according to a control map giving an exhaust opening ratio .theta..sub.e depending at least on the engine speed and the throttle valve opening ratio .theta..sub.th in order to control the pressure in the cylinder during up-stroke of the piston 8. The exhaust control valve 15 is formed by a thin shell-like member comprising an exhaust control portion 35 substantially along the cylinder curvature in the exhaust port 7 and wider than the whole width of the exhaust port and a swinging arm portion 34 for connecting at least a side of the exhaust control portion and the rotational shaft 33 perpendicular to the cylinder axis and accommodated in a receiving recess formed in the cylinder block. This receiving recess is communicated with the exhaust passage extending from the exhaust port 7 only in the working zone of the exhaust control portion.