This paper presents the experimental and analytical study on the temperature distribution and thermal deformation of the piston in diesel and gasoline engines.In order to predict temperature distribution and thermal deformation of piston, a finite element analysis has been carried out. The thermal boundary conditions around the pistion were assigned from analytical and empirical relation. The validity of the boundary conditions has been checked by the electric analogy method. Experimentally the piston temperatures for the running engine were measured by thermocouples using a mechanical linkage system and spring system.The predicted temperature distribution by a finite element method shows satisfactory agreement with the measured data. Also, for thermal deformation, steel strut and slot in piston have been analyzed by axi-symmetric 2-dimensionai finite element method using the virtual element addition method and experimental method.