Effect of phantom material on backscattered radiations was studied for photon irradiation. Monte Carlo calculations using MCNP-4B code were performed to analyze scattered radiation on the surface of 30×30×15 cm3slab phantoms with different material. Dose on the surface of a human body was also estimated with a modified MIRD-5 type phantom. No significant difference of dose due to scattered radiation was observed between a soft tissue slab phantom and the water-filled slab phantom recommended by the International Organization for Standardization. On the other hand, dose on the surface of the PMMA phantom was found to be larger than doses on the phantom with water or soft tissue. The results also showed that response of dosimeter on the ISO phantom would be near to that on the trunk of a human body.