In this study, GATE as a Monte Carlo code is used for calculation of gamma ray attenuation coefficient of some granite samples at 662, 1173.2 and 1332.5 keV photon energies. The simulated results of mass attenuation coefficients were compared with the experimental and theoretical data given in previous study. Satisfactory agreement has been observed between the GATE code and XCOM results. Differences between experimental and theoretical results were between 0.7% and 14.7%. This can be explained by experimental error.