Vinylglycine (2) has been shown to undergo racemization under acidic conditions. Optically pure 2 was obtained from 2·HCl by enzymatic hydrolysis through N-acetylvinylglycine (5), followed by recrystallization. (S)-N-(Methoxycarbonyl)vinylglycine (6) was configurationally so unstable under acidic conditions that 6 could not be obtained from 2 in an optically pure form. On the other hand, configurationally stable (S)-N-(9-phenylfluoren-9-yl)vinylglycine methyl ester (9) was synthesized from (S)-homoserine; 9 was hydrolyzed with sodium hydroxide to afford the carboxylic acid 10 of more than 99% ee.