ABSTRACT Gamma radiation-induced degradation of methylene blue (MB) in aqueous solution was studied for two groups: one with suspension of Titania, TiO2, photo-catalyst and the other without it. Degradation of methylene blue by gamma-rays (doses range: 200-1000 Gy) was investigated by measuring the change of absorbance spectrophotometrically at λmax= 661 nm. Initial pH of solution (values 5, 7 and 9) was considered as a basic factor to study. The changes of pH values for irradiated methylene blue solutions with respect to gamma dose were recorded. Post irradiation effect was determined by measuring absorbance after 24 hours. For both groups, the color of methylene blue was bleached gradually with dose indicating its degradation. It was found that presence of TiO2 causes more bleaching. Also, as initial pH increases, the degradation increases. Methylene blue IR spectra, before and after irradiation, were recorded to investigate the effect of gamma radiation on MB.