Regarding the serum phenol oxidase (PO) of the Macrobrachium rosenbergii, "South Tailake No.2" as the material, the properties of PO were studied by using L-DOPA as the reaction substrate and spectrophotometer to determine the PO activity under different temperature and pH conditions. The results showed that the temperature of PO activity was highest at 25°C, Activity decreased gradually below and above 25°C. The serum PO with vitality when the pH ranged from 5 to 8.4 and the best pH was 6. Therefore, the optimum parameters for the determination of PO activity of Macrobrachium rosenbergii were the reaction medium with pH 6 as the reaction medium at 25.