The pathology and tissue concentrat ion of the chronic olaquindox poisoning in common carp, Cyprinus carpio , were studied. The test was conducted for 90 days, with doses of 10, 25, 50, 100, 150 and 200mg#kg- 1 feed. The morbidity and mortality were 17. 5% , 27. 5%, 35. 0% , 42. 5%, 47. 5% , 55. 0% and 5. 0% , 10. 0%, 12. 5% , 17. 5% , 20. 0%, 30. 0% respectively. The clinic symptom of the poisoned fish was characterized by / the stress hemorrhage syndrome0. The lesions of poisoned cases showed hyperplasia, degeneration , necrosis and desquamation in the gill lamella epithelia, fatty or vacuolar degeneration and necrosis in the liver cells, the catarrhal enteritis, vacuolar degeneration in renal tubular epithelial cells, cardiac muscle cells and the adrenal gland cells. Ultrastructurally, the mitochondria of the cardiac muscle cells, the liver cells and renal tubular epithelial cells were swollen with disintegration and lysis of caritas. The fat drops increased in liver cells. The intestinal epithelium microvillis collapsed and desquamated at the first stage of the test , and then many intestinal epitheliums necrosed and desquamated. Hematologically , the Hb concentration and the RBC numbers dropped; the serum AST and ALT activity were raised. The olaquindox concentration in the liver, kidney and muscle of the test groups was signif icantly different from the control group.