Microorganisms capable of cleaving the urethane bond of t-butoxycarbonyl (Boc amino acids in a whole-cell reaction were screened among stock cultures, and Corynebacterium aquaticum IFO12154 was the most promising, The conversion of Boc-Ala to Ala was stimulated by CoSO4 in the medium and reaction mixture. The optimum whole-cell concentration was 25 mg lyophilized cells/ml. Boc-L-Met was the best substrate for this reaction, and other Boc-L-amino acids, as well as benzyloxycarbonyl-L-amino acids with hydrophobic residues, were also good substrates. Boc-D- and Z-D-amino acids were inert, When the reactions had proceeded for 24 h with each substrate at 10 mM, the molar conversion rates from Boc-L-, Dr-and D-Met were 100%, 50%, and 0% respectively, From 150 mM BOC-L-Met, 143 mM L-Met was formed at a molar yield of 95.3%.