Piston profile has a substantial effect on engine performance. A new method of determining piston profile, using composite materials, has been developed.In this method, preliminary piston surfaces are coated with the composite materials which have excellent characteristics with respect to thermal resistance, adhessiveness and lubrication. After being subjected to piston marking test, the composite material remaining on the piston defines a new piston profile. This new method gives a piston profile which has much reliability against scuffing, oil consumption and greater reduction in engine noise, friction and emission. And also this method makes it possible to evaluate quantitatively the piston profile correction after marking test and to shorten the profile developing time, compared with conventional testing methods.