Radiation-induced reaction of sulfuric acid with silica gel (SG) was carried out using ɤ-radiation from a 60Co source at room temperature and, its mechanism were suggested. The formation of sulfonated SG (SiO2-SO3H) was confirmed by IR, thermal analysis (TGA/ DSC). Elemental analysis and morphological structure of treated SG (SGtreated) was investigated by scanning electron microscopy (SEM). According to the comparison of the SEM images of SG and SGtreated , it seems that, irradiation of SG in the presence of sulfuric acid leads to partial segmentation of SG particles. The IR spectra of the treated silica (SGtreated) is different from that of the SG. Where, peaks related to the presence of sulfunic group are observed, as well as shifts of SG peaks due to treatment. Also, TGA/ DSC of SGtreated is different from that of SG. Elemental analysis reveals that particle size of SG affects the S/O % value, where SGtreated with >0.16mm - 0.2mm particle size has the maximum value. Also, S/O% value, of >0.16mm - 0.2mm SG particle size, increased, linearly, with absorbed dose up to 80 kGy and then decresedat higher doses.