Solar Energy and Photochemistry Laboratory, Department of Chemistry, University College of Science, M. L. Sukhadia University, Udaipur-313 002, Rajasthan, India E-mail : ameta_sc@yahoo.com, vaishnave.prahlad@gmail.com Department of Chemistry, M.P. Government P.G. College, Chittorgarh-312 001, Rajasthan, India Manuscript received 06 May 2010, revised 19 May 2010, accepted 27 July 2010 The oxidation using sono-photo-Fenton has been found to be a promising treatment for the effective decolorization and degradation of dye. The degradation of methylene blue was investigated using photo-Fenton and sono-photo-Fenton processes. The effect of different variables like the concentration of ferric ion, concentration of dye, pH, hydrogen peroxide, light Intensity etc. on the reaction rate has been observed and optimal conditions determined. The methylene blue dye degradation was found to depend on these variables. The progress of dye degradation was observed spectrophotometrically. The sono-photo-Fenton reaction showed higher degradation rate of the dye as compared to photo-Fenton process. The results showed that the dye was completely oxidized and degraded Into CO2 and H2O. A suitable tentative mechanism for degradation of methylene blue by sono-photo-Fenton's reaction has been proposed.