The decomposition rate of oxalate by hydrogen peroxide has been investigated by a KMnO 4 titration method. The rate equation for decomposition of hydrogen peroxide in the aqueous phase is 1n([H 2 O 2 2 O 2 ] 0 ) = -k 1 t, where k 1 =0.2, for [H + ] < 2M, k 1 =0.2+0.34 ([H + ]-2), for [H + ] > 2M. As the acidity increases over 2M, an acid catalysis effect appeared. The new rate equation proposed for the decomposition of oxalate by hydrogen peroxide is-d X [ O X ] = k 2 [H 2 O 2 ] 0 (1-X [ O X ] )(e - k 1 t - [OX] 0 2 O 2 ] 0 X [ O X ] ) 2 , increased with nitric acid concentration and the effect of hydrogen ion concentration was expressed as k 2 = a [H + ] n , where the values for a and n were a=1.54, n=0.3 at [H + ] < 2M, a=0.31, n=2.5 at [H + ] > 2M, respectively.