N-acyl-DL-3-(3,4-dihydroxyphenyl)serine or a catecholic hydroxyl-protected derivative thereof is stereospecifically de-acylated by reaction with a microorganism of the genus Streptomyces or Streptoverticillium having an acylase or with an extract of said microorganism containing said acylase, to produce L-3-(3,4-dihydroxyphenyl)serine or the hydroxyl-protected derivative thereof, with the N-acyl-D-3-(3,4-dihydroxyphenyl)serine compound remaining unaltered. The L-3-(3,4-dihydroxyphenyl)serine compound so produced can be separated from the N-acyl-D-3-(3,4-dihydroxyphenyl)serine compound owing to the difference in the properties of them.