In order to explore the effect of high temperature or cigarette smoke and their combined effect on the development of nervous system in early rat embryos, pregnant rats at the 8-11th day of gestation were exposed to high temperature and water soluble substances of cigarette smoke. All indexed of embryonic nervous system development were determined with experimental treat logical methods. The results showed that following the increase of temperature or cigarette smoke exposure all indexes correlated with embryonic nervous system development and morphological differentiation were changed, with an apparent dose-effect relationship (P < 0.01). The changes were related to specific phase of embryonic development. The results showed also that the nervous system development and morphological differentiation induced by both high temperature and cigarette smoke were higher than that by any single factor.