It is proposed that the nickel hydride phase in the nickel matrix can be identified by the difference in contrast by optical microscope observation. The ratio of the observed dark regions, compared to the light regions, correlated with the ratio of the integrated intensity of the X-ray diffraction profile of hydride to nickel during the decomposition process of hydride formed by electrochemical cathode charging of hydrogen in pure nickel. The identification of nickel hydride in the present work concludes that the depth of hydride formation is different between crystal grains.