Optically active 3-trimethylsilylalanine (TMS-Ala) was prepared by hydrolysis of N-acetyl-DL-TMS-Ala catalyzed by acylase I (aminoacylase; N-acylamino-acid amidohydrolase, EC 3.5.1.14). Acylase I from porcine kidney (PKA) was found to be more effective than that from Aspergillus melleus in the preparation of L-TMS-Ala. Under the optimized conditions, optically pure L-TMS-Ala (>99% enantiomeric excess, eel was obtained with a 72% yield. Furthermore, a highly optically pure D-TMS-Ala (96% ee) could also be obtained with a 76% yield by chemical hydrolysis of the residual substrate. Enzymatic synthesis of peptides containing TMS-Ala was also attempted in ethyl acetate. Benzyloxycarbonyl (Z)-L-TMS-Ala served as the substrate for thermolysin, whereas L-TMS-Ala-OMe was inactive as the amino component. In the case of inhibitory activity of dipeptides toward thermolysin, L-Leu-(L-TMS-Ala) was found to be a more potent inhibitor than L-Leu-L-Leu, which is known to be one of the most effective inhibitors of thermolysin among the dipeptides consisting of natural amino acids.