PURPOSE: To enable alkylation of a carbonyl compound in high efficiency, by reacting a carbonyl compound in the presence of a Lewis acid using an alkyl lead as an industrially advantageous alkylation agent having excellent stability, storability and handleability.

CONSTITUTION: Alkylation of a carbonyl compound is carried out by reacting (A) a carbonyl compound such as acetaldehyde, propionaldehyde, dimethyl ketone and diethyl ketone with (B) an alkyl lead, especially a tetraalkyl lead of formula R41Pb (R1 is alkyl or cycloalkyl; 4 R1 groups may be same or different) (e.g. tetraethyl lead) as an alkylation agent in the presence of (C) a Lewis acid (e.g. TiCl4, TiBr4 and BF3). The product is e.g. 1-phenylpropanol or 3-decanol and the process can be effectively used for the production of a hydroxyl compound or a halogenated compound having alkyl group.