Nanosize crystalline TiO2 and SiO2/TiO2 mixed oxide particles as a photocatalyst for rhodamine B dye (RB) degradation in aqueous media were synthesized by a hydrothermal process at 200 degrees C. They were characterized using XRD, SEM, FT-IR, UV/VIS and BET analysis. The effects of silica content on the crystallinity and photocatalytic activity of TiO2 were invetigated. Photocatalytic activity of the nano-TiO2 was compared with that of SiO2/TiO2 mixed oxies at the same conditions for degradition of RB, and mixed oxide catalysts showed more effective catalytic activity than the TiO2. The results revealed that photodegradation of RB proceeds by pseudo-first-order reaction kinetics where the rate constant, k, for degradation of 30 mg/L RB using the catalyst with 0.05 SiO2/TiO2 mole ratio is 0.133 min(-1).