The combination of a Rh(II) salt and a Lewis acid, Sc(OTf)(3), as a highly active and robust cooperative catalyst system for ketone hydroacylation was developed. The catalyst system showed high turnover numbers (up to ca. 400) even under air, whereas the corresponding Rh(I)/Sc(OTf)(3) system did not work well. The application of the Rh(II)/Sc system was also extended to hydroacylation of olefins and an enantioselective reaction.