Abstract: In order to determinethe accumulation of olaquindox in common carps(Cyprinus carp)and prussian carp(Carassius auratus gibelio), these two kinds of fishes were fed with diets which contented the olaquindox at the doses of 350mg/kg and 400mg/kg respectively, and the method for the determination of olaquindox residues in flesh for export (SN0197-94,An industry standard for export in the People. s Republic of China) and high performance liquid chromatography(HPLC) was used.The experiments were conducted for 99 days. Culture styles included monocultureof prussian carp, polycultureof prussian carp and common carp.The results showed that, of the three selected organs(liver, kidney and muscle), the accumulation of olaquindox in the liver was the highest, followed by the kidney and the muscle. On the 99th day, olaquindox. s concentration in the livers was 10.057 0.015(3)mg/kg in prussian carp of monocultural groups, which was 10.1070.226 (3) mg/kg in prussian carp and was 9. 883 0.032(3) mg/kg in common carps of polycultural group. Those in the kidneys respectivelywere: 7149401064(3)mg/kg, 7.7770.138(3)mg/kg, 7.6080.086(3)mg/kg and 0.17001003(3)mg/kg, 0.1600.003(3) mg/kg, 0.486006(3)mg/kg in the muscles.Although relative growth rate in the polycultural carps were 102. 7% and 110.7% respectively,their anti stress ability wasreduced apparently with the increasing intake of olaquindox. After the stimulation were administered, the stress rate of prussian carp in monoculture climbed from 44. 8% on 58d to 64. 3% on 99d, that of prussian carp and common carps in polyculture climbed from 66. 7% and 46. 2% on 58d to 88. 3% and 76. 9% on 99d.Nomatter on 58d or on 99d,there are significantly different between the control and test groups(P0.05). It. s observed that the number of the inflammatory cells grew, the volume of the cell shrank, and the cel- l nuclear lessened. It was found that extensively granular and vacuolar degeneration and necrosis of liver cells in every test groups. Renal tubule cells degenerate and capillary dilate.The net crossing membrane of spleen festers and the structure of spleen were destroyed seriously.The distinction between each two cells became obscure.Histopathology indicated the following changes: tissues of disease fisheswere hemorrhage, their cells appeared edema and necrosis. Which caused extensive tissue damage, blood vessels were enlarged and seriously damaged.A large number of erythrocytes in the blood vessels and tissues were deformed, broke and haemolyzed. The study showed that olaquindox is toxicto cultural fishes and must be forbidden in aquaculture.