EFFECTS of silica gel (SG) and its particle size on the radiation-induced electrical conductivity (RIC) and pH of pure water were studied. RIC of pure water in the absence of SG increases as absorbed dose increases. In the presence of SG the values of the RIC are higher than the corresponding values in the absence of SG up to 12.28kGy, which reflects the induced catalytic effect of irradiated SG. Moreover, the particle size of SG seems to affect the RIC of water. Therefore, as the particle size decreases, the RIC increases (below18.99kGy). Also, it was observed that the pH values decrease as the RIC increases and vice versa. The RIC and variation of pH in the studied samples are related to the radiation induced formation of H2O2 and H3O2+. The induced catalytic effect of SG is related to the radiation-induced formation of electron/ +ve hole (e/ h+) pair during ɤ-radiolysis of SG. Therefore, the RIC increases (pH values decrease) as particle size of SG decreases (surface area increases).