The technique of transmission electron microscopy combined with enzymatic methods was used to analyse the variations of the immune-related enzymes activity in hepatopancreas,gills and muscles,and to compare the morphological changes of the hepatopancreas and gills of redclaw crayfish, Cherax quadricarinatus, under different concentrations of nitrite stress.The results showed that the activity of ACP,AKP,SOD and GSH-PX in three tissues under the stress of nitrite were significantly lower(P<0.05)compared with control group; with the increase of the nitrite concentration,the activity of enzymes was decreased gradually substantially; the activity of Na ,K -ATPase and Ca² ,Mg² -ATPase in gills was also decreased with the increase of nitrite concentration.Ultrastructure analusis showed that the cuticle of gills was damaged or even disintegrated with the increase of nitrite concentration; epithelial cell was loosely arranged,and the phenomenon of vacuolization was emerged; morphological changes were also obviously found in organelles; the phenomenon of vacuolization was emerged in haemocoel,and hemocytes were deformed.Hepatopancreatic epithelial cells were arranged in haphazard,or even with cell lysis and severe vacolation phenomenon; microvilli were structural damaged,some broken,the distance between the hepatopancreatic tubules was expanded,connective tissues became thin,and hemocytes deformations were found; in high concentration,the lipid droplets of R cells were reduced,nuclear membrane was disintegrated,cell membrane was ruptured and vacolation was increased; in F cells,the rough endoplasmic reticulum was reduced,smooth endoplasmic reticulum was increased,ribosomes was decreased,vacolation was increased and endoplasmic reticulum edema was emerged.In summary,the activity of immunerelated enzymes was influenced by the nitrite stress,and the morphological structures of the hepatopancreas and gills were also affected,as well as their biological functions.