To provide a partially strengthened piston of light weight, excellent in wear resistance and high temp. fatigue strength and a manufacturing method thereof at a low cost.

This partially strengthened piston is an Al base reactive composite material composed of the component for improving the wear resistance by chemical reaction with a piston base material and whiskers or long fibers for improving the high temp. fatigue resistance. Further, the manufacturing method of the partially strengthened piston is executed by inserting the Al base composite material after aluminizing with the Al or Al base piston base material during liquid state or solid-liquid coexisting state of the Al layer on the surface of the Al base composite material.