Ornithine decarboxylase (EC 4.1.1.17) was purified to homogeneity from soybeans, Glycine max, axes by chromatographic separations on DEAF-Sephacel, Hydroxyapatite and phenyl-Sepharose with the addition of 15% glycerol. The molecular weight of the enzyme estimated by Sephacryl S-300 gel filtration and SDS-PAGE was 55,000 daltons and monomeric. The optimal pH and temperature were 8.5 and 40℃, respectively, and K_m was 0.135 mM. Carbonyl group and cysteinyl residue seem to be involved in enzyme activity. DFMO was a potent suicide inhibitor while metal ions, agmatine and polyamines were innocuous for the enzymatic activity.