Different concentrations (0.1, 3, 6 M) of urea aqueous Solutions (UAS) have been irradiated with 60Co- ɤ-rays in the presence of silica gel (SG) with different particle size (0.1-0.5mm) at room temperature. The radiation induced electrical conductivity (RIC) of the irradiated solutions was measured. The RIC values of the 0.1 M solutions increase as the particle size of SG decreases i.e., the particle surface area increases. This observation points to a radiation induced chemical reactions, which are catalyzed by SG. These reactions, probably, yield products, which increase the RIC such as urea peroxide (UP). On the other hand, different behavior was observed in the case of 3, 6 M solutions, where, the RIC increases as particle size increase. So, the mechanism of production of the species which increase the RIC of 0.1 M samples is different than that in the case of 3, 6 M. In all irradiated samples the pH values tend to increase slightly as particle size increases. A mechanism was proposed to explain the obtained data.