PURPOSE: To produce a penem compound useful as an antibacterial agent in high yield and purity by the enzymatic hydrolysis of a penem ester with a lipase or an acylase in an alcoholic solution.

CONSTITUTION: A penem ester of formula I (R1 is H or a 1-6C alkyl; R2 is H, a 1-18C alkyl, an alkenyl, phenyl, a phenylalkyl, a phenylalkenyl or an alkoxy) is subjected to enzymatic hydrolysis with a lipase or an acylase in an alcoholic solution. A penem compound of formula II (R is carboxyl or carboxylic acid anion) can be produced by a simple solvent removal process and the direct crystallization of raw materials.