The present study was conducted to obtain information on the effects of amitraz on reproductive and developmental parameters in rats. The test chemical was administered via the drinking water containing 0, 40, 120, and 360 ppm to male rats from 2 weeks before mating to the end of 14-day mating period and to females from 2 weeks before mating, throughout mating, gestation and up to lactational day 4. During the study period, clinical signs, body weights, food intake, organ weights, reproductive and littering findings, necropsy findings, sperm parameters, and histopathology were examined. At 360 ppm, decreases in the body weight gain, food consumption, and the number of live pups and an increase in the post-implantation loss were observed. In addition, decreases in the seminal vesicle weight and sperm motility were found in males. At 120 ppm, a decrease in the food consumption was found transiently in both males and females, but no reproductive and developmental toxicity was observed in both sexes. There were no signs of either general or reproductive and developmental toxicity in the 40 ppm group. Based on these results, it was concluded that the repeated oral administration of amitraz to rats resulted in a decrease in the food consumption at 120 ppm and decreases in the seminal vesicle weight, sperm motility, and the number of live pups and an increase in the post-implantation loss at 360 ppm in rats. Under these experimental conditions, the no-observed-adverse-effect level (NOAEL) of amitraz for general and reproduction/developmental toxicity was believed to be 120 ppm, and the no-observed-effect level (NOEL) of amitraz was believed to be 40 ppm in rats.