PURPOSE: To obtain a lactone useful as a solvent and an intermediate with high selectivity without forming a byproduct by reacting a specific (substituted) alkenol and carbon monoxide-containing gas by using a specific catalyst.

CONSTITUTION: A (substituted)alkenol represented by formula I (wherein m and p are each 0 or 1; n is 0-25; Q1 is H or 1-20C alkyl; Q2-Q5 are each H or 1-4C alkyl and, when p is 1, m is 1 and both of Q1-Q5 are H and at least one of Q3 and Q4 is H and, when p is 0, n is 0 and Q1 is H)(pref., 3-butenol represented by formula II or 4-pentenol represented by formula III) is reacted with carbon monoxide-containing gas by using a catalyst system obtained by combining a palladium compd. [pref., palladium (II) 12 or less C alkanoate] (A), phosphine, arsine or stibine (B) and a protonic acid having pKa of below 2 (C) to obtain the objective lactone having 4-5 C-atoms in its ring.