Objective To investigate the effects of diflubenzuron on the blood system in rats. Methods A total of 80 rats were randomly divided into three diflubenzuron treated groups and one negative control group. Different doses of diflubenzuron at 0, 25, 500 and 10000 mg/kg were administered continuously for 90 days to the rats by the way of feeding. Animals were observed for clinical signs of toxicity, food consumption and body weight. Haematological parameters, clinical chemistry parameters, absolute and relative organ weights and histopathological changes were examined at the end of the study. Result During the period of the study, the food and water consumption were all normal at all dose groups and no obvious toxicity symptoms appeared. For haematological parameters, the main changes were the decrease of red blood cell count(RBC), haemoglobin(HGB) and haematocrit(HCT) in the medium and high dose groups and the increase of mean corpuscular volume(MCV) and erythrocyte hemoglobin distribution width(RDW) in the high dose group(P<0.05 or 0.01). For clinical chemistry parameters, the main change was the increase of total bilirubin(TBIL) in the high dose group of male rats(P<0.05). The absolute and relative spleen weights increased obviously in the female and male rats of the high dose group(P<0.01). The absolute and relative liver weights increased obviously in the female rats of the high dose group(P<0.01). The spleens were larger, harder and darker than normal in all of the rats of high dose group and part of the rats of medium dose group. For the result of histopathology examination of spleen, the main changes were a lot of red cells in the medullary sinus and haemosiderin in the medulla. Conclusion Diflubenzuron had toxic effect on the blood system of the rats. The spleen was intumesce and chronic hemolytic anemia may be occurred for long-term exposure.