Abstract: Macrobrachium nipponense,2.5-3g in body weight, was bought from aquaculture market in Wuhan, and then cultured in laboratory tank (65cm×45cm×34cm). The shrimps were kept in the tank for 7 days and fed with diet containing 1‰ Polysticus and Cordyceps polysaccharide. The haemolymph was then taken from the heart of M.nipponense. which were cultured for 1,4,7,14,21,28 days to determine the phenoloxidase (PO) activity. The results were as follows: 1 Acording to Wang Lei's method, the PO activity was 8.3 units/mL, while the PO activity was 290 units/mL by the Horowitz's method. Besides the high sensitivity, the latter had a better repetition than the former. Therefore, the Horowitz's method was better for responding the immune state of M.nipponense. 2. PO activity could be tested in the haemolymph of M.nipponense. There was little effect on the PO activity by adding SDS. It was clear that in the haemolymph PO was not present by the form of zymogen. 3. At high temperature (for example 23.8±3.8℃), M.nipponense had a vigorously ingestion, the PO activity of Polystictus and Cordyceps groups increased about 34.52% and 84.62%. Polystictus and Cordyceps polysaccharide had remarkable enhancement on the PO activity. While the increase of PO activity was 30.02% and 5.12%respectively in low water temperature. The enhancement of polysaccharide on the PO activity was not significant. The increase of PO activity indicated that Polystictus and Cordyceps polysaccharide could improve nonspecific immunity of the shrimps, which would be useful as a potential immunostimulant.