Abstract: Objective To study effect of ciprofloxac in on immunotoxicity and muscle quality in rats.Methods All rats in high,middle,low dose group(44,11,5.5 mg/kg)were admin istered with intrape ritoneal injection of cipro floxac in once a day,for 7 days continuously.The thymus and spleen coefficients were calculated and morphologic change of spleniclymphocyte was observed.The changes of muscle protein content and pH values were observed.Results Thymus and spleen coefficients(mg/g)in high and low dosage group were 9.1±2.3,6.3±1.1,respectively,and those of in the controll were 6.5±1.6,3.4±0.5.The contents of muscle prote in(g/100g)in high,medium,and low dose groups were 24.68±0.55,22.48±0.54,21.22±1.25,respectively,lower than that of the control(31.83±2.36,P<0.05).Paramorphia of lymphocyte in high dose ciprofloxac in treated group was observed.Conclusion Cipro floxacin has mimunotoxicity and could reduce muscle protein significantly in rats.