Diaminopimelate decarboxylase (E. C. 4.1.1.20) from Micrococcus glutamicus horn-, lysine excreting strain, is purified 350- fold by ammonium sulphate precipitation, gel filtration on Sephadex G-150, and chromatography on hydroxylapatite and DEAE-Seph adex. The enzyme has a molecular weight of 53000, isoelectric point of 4.3, optimal pH for activity 7.7, energy of activation 11.1 kcal/mol, and Km for substrate 1.26 mM. For its stability, the presence of pyridoxal phosphate and sulphydril reagent is necessary, and most catalytic activity is retained within a pH range of 5.5 to 8.5. Aminoacids, L-lysine, L-norleucine, L- u- aminoadipic, L-glutamic and L-aspartic acid, are inhibitors of diaminopimelate decarboxylase from M. glutamicus horn-.