Abstract: The haematological changes had been studied in common carp(Cyprinus carpio)by Subacute toxicity test of olaquindox. The test was conducted for 6 weeks,with the doses of 1000mg/kg、2000mg/kg、3000mg/kg feed respectively.The morbidity and mortality were 35%、70%、92.5% and 27.5%、57.5%、82.5%,respectively.The clinic symptom of the polisoned fish was characterized by "the stress hemorrhage syndrome."The haematological changes in the poisoned fish showed that the Hb concentration、the RBCnumbers、the red blood cell SOD activity and the serum sodium level dropped;the serum AST、ALT activity and the serum potassium level raised.These haematological changes of the experimental groups were different significangly from the control group.