This study was investigated to determine whether nicotine causes the morphological changes and expression of heat shock protein(HSP) 70 in the central nervous system of rat embryo. The pregnant rats were injected s.c. twice daily with 3 mg nicotine per 100g body weight from day 0 to 14 of gestation and embryos were removed on gestation day 15. As morphological changes, retardation of cell proliferaton was observed in the telencephalon of nicotine-treated groups and no changes in the other region were found. Minimal HSP 70 was expressed over chole central nervous system was similar between control and nicotine-treated group, the expression of blood cells in the meinges and chroid plexus was significantly greater in nicotine-treated group than in control.