Arginine Deiminase(ADI)was purified to homogeneity using ammonium sulfate precipitation, Q-Sepharose Fast Flow anion exchange chromatography and SephadexG-75 gel filtration chromatography. This purification protocol resulted in a 34.5-fold purification of ADI with 31.4% final yield. A molecular weight of about 190 kD determined by native gradient polyacrylamide gel electrophoresis. The enzyme has only one kind of 46 kD subunit determined by SDS-PAGE. Combining the results from the two kinds of electrophoresis, the authors deduce that the enzyme may be a tetramer. The optimum pH and temperature for lipolytic activity of ADI was pH 6.5 and 50℃, respectively. It was extremely stable at 45℃ and retained 97.9% of its original activity for 30 min. The stability declined rapidly as soon as the temperature rose over 50℃. ADI was highly stable in the pH range from pH 5-8. ADI acted on L-arginine but not on D-arginine. ADI catabolism was dependent on metal ions. At their adequate concentration, Mn2+, Mg2+ and Co2+ were the effective promoter, while superfluous Zn2+and Co2+ inhibited ADI activity. L-citrulline did not act on ADI, but L-ornithine inhibited ADI activity. The degradation of L-arginine with ADI catalysis was according to simple Michaelis-Menten equation. The Michaelis constant was 3.2686 mmol/L and the maximum velocity was 2.44 μmol/min.