Dyes as one of the majority critical environmental pollutants from industrial wastewaters, have caused many concerns for researchers. In this research an effective photocatalyst based on La₂O3-SiO₂ nanocomposite was prepared and evaluated for degradation of toluidine blue (TB) dye. The prepared photocatalyst was illustrated impressive performance in degradation of TB equal to 97% by visible light irritation. Accuracy of synthesized nanocomposite was studied by some technics including FE-SEM, FT-IR, EDX and mapping analysis. Also the effective parameters in degradation percent of TB such as pH, temperature, time, concentration and the amount of nanocomposite were investigated and optimized equal to amounts of 8.0, 25℃, 80 min, 3.0 µg/mL and 0.04 mg respectively.