To obtain a corresponding ester or lactone in high yield from a ketone using hydrogen peroxide.

This ester or lactone of formula II (Ra and Rb are each an organic group having a carbon atom at the binding site to the ad-jacent carbonyl carbon atom or oxygen atom, or may be bound to each other to form a ring together with the adjacent carbonyl carbon atom or oxygen atom) is obtained by reaction of a corresponding ketone of formula I (Ra and Rb are each an organic group having a carbon atom at the binding site to the adjacent carbonyl carbon atom, or may be bound to each other to form a ring together with the adjacent carbonyl carbon atom) with hydrogen peroxide in the presence of a compound having a metal element selected from the groups III XIII, XIV and XV ones.