The present study was undertaken to investigate the effect of ascorbic acid on the blood pressure of SHR in established phase. Twenty SHR at age of 23 weeks were divided into two groups; The control group and the ascorbic acid group in which 3 mg/kg/day ascorbic acid was orally administered for 10 weeks. The results obtained were as follows; 1) In the control group the systolic pressure(192.7±4.2 mmHg at O week) tended to increase gradually throughout the entire experimental period. 2) In the experimental group the systolic pressure(193.5±3.5 mmHg at O week) was generally lower as compared with that of control group. A significant difference in the blood pressure was observed between two groups at 3 rd and 4 th week of experimental period. Though it is impossible from the result of present study to elucidate the exact mechanism of blood pressure lowering effect of ascorbic acid, it is inferred that ascorbic acid may exert its effect at the vascular walls.