Abstract: In order to fully understand Lewisite’s potential toxicity and teratogenicity, its toxicological characteristics to rats in perinatal period were investigated. Three tests with high, middle and low doses of Lewisite Agent content defined separately as 0.650,0.325and 0.217mg/kg, were undertaken from the fifteenth day of pregnancy to the twenty-eighth day of lactation of the F0generation rats. Effects on the survival fraction, body weight, reflection behavior and reproductive function of female rats of the F0generation and filial rats of the F1generation were studied. Results showed that the maximum no observed adverse effect level (NOAEL) of Lewisite for filial rats the F1generation was 0.217mg/kg, while the lowest observed adverse effect level (LOAEL) was 0.325mg/kg. Consequently, the Lewisite in perinatal period had significant impacts on the physical activities of female rats and filial rats. The decease order of toxicity of the four warfare agents (Lewisite, Diphenylchloroarsine, Chloroacetophenone and Diphenylcyanoarsine) to perinatal period filial rats was:Lewisite (L)＞Diphenylchloroarsine (DA) ＞Chloroacetophenone (CN). Lewisite(L) and Diphenylcyanoarsine(DC), however, had no significant differences in the toxicity to filial rats during the perinatal period.