The photocatalytic degradation of a hazardous methylene green dye solution has been reported. The effects of various parameters such as catalyst loading, pH, initial concentration of the dye, concentration of H2O2 and K2S2O8, concentration of NaCl and Na2CO3, N-2 and O-2 bubbling, and intensity of light on decolourization have been investigated. The photocatalytic removal of methylene green dye and its, degradation efficiency has been evaluated by determination of reduction in the chemical oxygen demand (COD) from 440 mg/L to 5 mg/L and increase in CO2 values from 9 mg/L to 212 mg/L in 7 h. A decrease in pH and increase in conductivity of solution is observed with increase in the extent of mineralization. The extent of decolourization has been discussed in terms of the Langmuir-Hinshelwood model. The rate of decolourization of dye is recorded with respect to the change in the intensity of absorption peak in visible region. The prominent peak at lambda(max), i.e., 650 nm decreases gradually and finally disappears indicating that the dye is decolourized. Similarly the peak in the UV region at 300 nm decreases with the passage of time, thereby confirming the complete mineralization of the dye.