In the present study, Nilsson's venous outflow method was used to investigate the changes of cerebral blood flow(CBF)in aged and adult SD rats during cigarette smoking. In the aged rats,the CBF increased 25.7% and 36.1% of the control respectively after 1 min and 5 min smoking.While in the adult rats, the respective values are 22.7%and 107.8%. Blood pressure(BP),pHa and PaO2 were also observed to decrease after smoking, but PaCO2 is increased. Cerebrovascular responses to smoking were obviously smaller in the aged than in the adult rats, seemingly due to a weaker function of cerebrovascular regulation in the aged rats, owing to perhaps a decrease of β- receptor and a changes of cerebrovascular morphology.