A Ni-Co-P alloy containing a particle composite plating material of Si3N4 consists of metal anti ceramic and is called a metal matrix composite. Residual macro- and microstress are generated due to the misfit of the mechanical properties. Since residual stress affects the strength of materials, it is necessary to evaluate the micro- and microstress accurately. The influences of the volume fraction and grain size of Si3N4 on the residual stress in both the matrix and the inclusion phase were investigated. The effect of the film thickness in the phase stress was also examined. X-Ray data from both phases were used to verify that a relationship existed between plating conditions and the residual stress. Strains in the individual phases were measured using an X-ray diffraction technique. Phase stress was determined by using the X-ray elastic constants.