Permethrin, a synthetic pyrethroid insecticide, has been widely used to protect domestic animals and the public health, as well as in agriculture against a variety of pests, which provides potential for environmental exposure. Permethrin is classified as possible human carcinogen and endocrine disrupting chemical by many international authorities. However, its developmental effects have been rarely studied. This study investigated the effects of permethrin during embryo-genesis. Developmental toxicity of permethrin was evaluated using short-term in vitro battery system. Gestation day 9.5 rat embryos (organogenesis) were cultured with permethrin (0.1,0.4 and 0.8 mg/ml) for 48 hours using whole embryo culture system. All the treatments exhibited significant decreases in the total morphological score. Permethrin induced significant growth retardation and the developmental abnormality at doses of 0.4 and 0.8 mg/ml. Moreover, the DNA and protein contents of embryos decreased in dose-dependent manner. These observations suggest that permethrin contributes to toxicity on embryonic developments in rats.