This experiment was performed to determine the antihypertensive effect of Yangganhwadam-tang(YHT) on hypertension in spontaneously hypertensive rat. The results obtained were as follows : 1. YHT showed scavenging activity on DPPH free radical and SOD-like activity. 2. YHT significantly decreased heart weight. 3. YHT significantly decreased blood pressure and pulse. 4. YHT significantly decreased the level of plasma aldosterone. 5. YHT significantly decreased the level of norepinephrine. 6. YHT significantly decreased the levels of potassium and calcium. 7. YHT significantly decreased the level of BUN. 8. YHT decreased eosinophilic changes in the heart cells, and dilated renal arterioles stenosis. These results suggest that YHT might be effective in treatment and prevention of hypertension.