The direct addition of various beta-dicarbonyl compounds to a series of secondary alcohols and alkenes has been achieved using 1 mol % perchloric acid (HClO(4)) as the catalyst. The HClO(4)-catalyzed reactions could be conveniently conducted in commercial solvent and gave moderate to excellent yields. Moreover, the silica gel-supported HClO(4) could also catalyze the heterogeneous addition for a series of substrates with similar or even higher yields in comparison with the homogeneous ones. The supported catalyst could be readily recovered and reused for four runs. Furthermore, the mechanism of the HClO(4)-catalyzed addition of the beta-diketone to alcohol was investigated, and an S(N)1 mechanism was proved unambiguously for the first time through a series of experiments. The discrimination of catalytic abilities among different Brønsted acids was also rationalized by DFT calculations.