Semi-purified lipases from Candida rugosa, Pseudomonas cepacia and Alcaligenes sp. were chemically modified with a wide range of hydrophobic groups such as benzyloxycarbonyl, p-nitrobenzyloxycarbonyl, p-methoxybenzyloxycarbonyl, t-butoxycarbonyl, lauroyl and acetyl moieties. The Candida rugosa lipase MY modified with the benzyloxycarbonyl group (modification ratio = 84%) brought about a 15-fold increase in enantioselectivity (E value) towards the hydrolysis of racemic butyl 2-(4-ethylphenoxy) propionate in an aqueous buffer solution, although the enzymatic activity was decreased. The origin of the enantioselectivity enhancement by chemical modification of the lipase is attributed to a significant deceleration in the initial reaction rate for the incorrectly binding enantiomer.