A catalytic amount of RuCl3 in the presence of excess of N-methyl-morpholine N-oxide (NMO) in DMF oxidizes secondary alcohols to ketones. Spectral studies reveal the formation of a Ru(V)-oxo species which is formed in situ on adding N-oxide. The formation of Ru(V) has been established by cyclic voltammetric studies. The mechanism involves the formation of Ru(V)-oxo species in steady state concentrations from Ru(III) and NMO, and this in turn reacts with the substrate in the rate-determining step. © 1987.