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Arginine decarboxylase (E.C. 4.1.1) after purification from rice seedlings was separated into fractions A (MW88000) and B (MW174000) by gel chromatography. Fraction B was much more active than A. After DEAEcellulose chromatography, the active fraction of the enzyme (B) was purified to homogeneity, which appeared as a single band in gel electrophoresis. The optimal pH and temperature for the enzyme were 8.0 and 45°C, respectively. The enzyme followed typical Michaelis-Menten kinetics with a Kmvalue of 0.28mM. It had no dependence on a metal, and consisted of 16 amino acids of which proline was prominent. Pyridoxal-5-phosphate acted as a cofactor of the enzyme. The enzyme activity was inhibited by various amines and inhibitors, of which the highest inhibition was obtained with spermine and hydroxylamine. The plant hormones played a vital role in regulating the activity of the enzyme which was promoted by kinetin and inhibited by abscisic acid.