A novel enzyme, N-acylamino acid racemase (acylamino acid racemase) which catalyzes the interconversion of the enantiomers of N-acylamino acid, but does not act on amino acids, was found in an actinomycete strain Y-53 isolated from soil. A taxonomic study on the strain identified Y-53 as a strain of Streptomyces atratus. This strain also produced l- and d-aminoacylases simultaneously. Furthermore, another 13 strains of actinomycetes with the enzyme activity from the type culture collection of the Institute for Fermentation, Osaka (IFO) were observed.