Permethrin, a type I synthetic pyrethroid insecticide, was evaluated through assessment of the behavioral development of F1 progeny of mice. Groups each of 30 male and 30 female ICR (CD-1) mice, as F0-generation, were given 0, 4.9, 9.8, and 19.6 mg/kg/d permethrin by gavage for 4 weeks before mating. Behavioral endpoints of motor reflexes, motor coordination, and activity were evaluated in F1 progeny. Clinical signs of toxicity including salivation, hyperactivity, and liquid feces which attributed to permethrin were observed in the F0-mice treated with 9.8 and 19.6 mg/kg/d. Reduction of body weight became evident only during gestation and lactation periods for the middle and high dose groups. Significant differences in the development of reflexes, swimming ability, and open field activity were evident in the offspring for the 9.8 and 19.6 mg/kg/d dose groups compared to the control group. These results show that permethrin at dose levels of 9.8 and 19.6 mg/kg/d can induce a significant risk to the offspring following treatment of F0-mice before mating. The NOEL obtained in this study for the effects of permethrin on the development of the F1-progeny is 4.9 mg/kg/d.