Abstract: The catalytic effect of bis-(acetonylacetonato) cobalt(Ⅱ) in the C-alkylation of acetylacetone was investigated. Acetylacetone and benzyl or substituted benzyl chloride were heated in o-dichlorobenzene solution in the presence of catalytic amounts of bis-(acetonylacetonato) cobalt(Ⅱ), giving mainly C-alkylation products. Seven new compounds were pre pared by this method. Electron donating groups in the para position of substituted benzyl chlorides accelerated the alkylation reaction and gave higher yields.