OBJECTIVE: To investigate the chronic toxicity and carcinogenicity of kresoxim-methyl in rats. METHODS: Specific pathogen free SD rats were randomly divided into control group and low-, medium-and high-dose groups according to the body weight of rats, 120 rats in each group with half male and half female rats. The chronic toxicity and carcinogenesis was induced in rats for 104 weeks by oral feeding. The dose of kresoxim-methyl in feed of male and female rats was 0, 75, 300 and 1 200 mg/kg. During the process of experiment, the body weight of rats was weighed. The blood biochemistry, organ coefficient and histopathology were examined at the end of the exposure, and the tumor incidence was calculated. RESULTS: There was no significant difference in mortality of the female or male rats in the four groups(P>0.05). At the 32 nd, 48 th and 56 th week after exposure, the body mass of female rats in the high dose group was lower than that in control group(P<0.05); at the 8 th, 16 th, 24 th and 32 nd week, the body mass of male rats in the high dose group was lower than that in the control group(P<0.05). The organ coefficients of heart and adrenal gland of female rats in the high dose group were higher than those in the control group and the low dose group(P<0.05). The organ coefficient of liver of male rats in the high dose group was lower than that in the control group(P<0.05). The alkaline phosphatase of male rats in the three dose groups was lower than that in the control group(P<0.05). The blood glucose of male rats in the high dose group was higher than that in the control group(P<0.05). The aspartate aminotransferase of male rats in the high dose group was lower than that in the control group(P<0.05). There was no significant difference among the three indexes in female rats(P>0.05). The tumor incidence of the control group and the low, medium and high dose groups were 68.3%, 75.0%, 75.0% and 78.8%, respectively, with no significant difference(P>0.05). The tumor incidence of the female rats was higher than that of the male rats(87.0% vs 61.5%,P<0.01).The tumor multiplicity of the above four groups were 38.3%, 35.8%, 35.0%, 39.8%, respectively, with no significant difference(P>0.05). The tumor multiplicity in female rats was higher than that in male rats(56.9% vs 17.6%,P<0.01). CONCLUSION: The no observed adverse effect level of kresoxim-methyl to female and male SD rats was 24.726 and 20.002 mg/(kg·d), respectively. No carcinogenicity of kresoxim-methyl to SD rats was observed.