A plasma ignition system for an engine having any number of engine cylinders, which comprises: (A) a plurality of plasma ignition plugs each mounted within a corresponding engine cylinder; (B) a first power supply unit for supplying a first electric power into each plasma ignition plug so as to generate a spark discharge within each plasma ignition plug; (C) a first switching circuit for sequentially connecting the first power supply unit to each plasma ignition plug according to a predetermined ignition order; (D) a second power supply unit for supplying a second electric power into each plasma ignition plug so as to generate a high-temperature plasma gas within each plasma ignition plug; and (E) a second switching circuit for sequentially connecting two of the plasma ignition plugs within the respective engine cylinders, one engine cylinder being at the start of an explosion stroke and the other engine cylinder being at almost end of an exhaust stroke, in a predetermined delay after the occurrence of the spark discharge at the corresponding plasma ignition plug when the engine speed is below a predetermined value, so that the number of high-voltage withstanding characteristic capacitors and switching elements (thyristors) of the switching circuits can be reduced half that of engine cylinders and the power consumption of these first and second power supply units can be saved remarkably particularly when the engine speed exceeds the predetermined value, e.g., 3000 r.p.m.