Objective To study the toxicity of fosthiazate feeding for 90 days in rats, and to determine the maximal non-effective dose of fosthiazate, in order to provide the reference dose for safety in production and chronic toxicity experiment. Methods A total of 80 SD rats (half female and half male) were randomly divided into 4 groups, respectively: 0.8 mg/kg·bw·d group, 4.0 mg/kg·bw·d group, 20.0 mg/kg·bw·d group, and normal control group. The rats were sacrificed to determine the indices including serum biochemical parameters, body weight, routine urine test and organ coefficients after the end of the experiment, and the results were statistically analyzed. Results In the high dose group, the body weight gain was slowed in male and female rats. The TG and CHE in the high dose group of male rats and the TP, ALB, CREA, GLU, and CHE in the high dose group of female rats were significantly lower than those of normal control group. The ALP in the high dose group of female rats was higher than that of the normal control group. The positive rates of BIL, SG, and PRO in both male and female rats had significant differences compared with those of normal control group. The organ coefficients of brain, lung, kidney, adrenal, and testis of male rats, and the organ coefficients of brain, lung, and kidney of female rats in the high dose group were significantly higher than those of the normal control group. The ovaries and uterus in the female rats of high dose group were significantly lower than those of normal control group(P<0.05，P<0.01). Conclusions The oral dose of fosthiazate at 4.0 mg/kg·bw·d fed for 90 days and above cause toxic effects on rats, and its maximal non-effect dose of long-term intake of low-dose fosthiazate on rats is 4 mg/kg·bw·d.