Department of Chemistry, 1. N. V. University. Jodhpur-342 005. Rajasthan, India E-mail : drpkvs27@yahoo.com RD National College, Bandra West, Mumbai University, Mumbai-400 050. India Manuscript received 28 January 2008, revised 24 March 2009, accepted 1 April 2009 The oxidation of a few unsaturated acids viz. maleic, fumaric, crotonic and cinnamic acids by tetrakis (pyridine) silver dichromate (TPSD) in dimethylsulphoxide (DMSO) leads to the formation of corresponding epoxide. The reaction is or first order with respect to TPSD and the acid. The reaction is catalysed by hydrogen ions. The hydrogen-ion dependence has the form : kobs = a + b [H+]. The oxidation of these acids was studied in nineteen different organic solvents. The solvent effect was analyzed by Kanllet's and Swain's multiparametric equations. Solvent effect indicated the importance of the cation-solvating power of the solvent. A mechanism involving a three-centre transition state has been postulated.