Abstract: Objective To study the effect of metformin on blood pressure in patients with metabolic syndrome（MS）. Methods Eighty-seven patients of MS with mild essential hypertension and fasting plasma glucose（FPG） 6.1—8.0 mmol/L or 2 hour plasma glucose（2 h PG）7.8—12.0mmol/L were randomly assigned to receive low-fat diet （n=43） or low-fat diet plus metformin 0.25, tid for 24 weeks. Blood pressure and insulin resistance, serum lipid were determined before and after 24 weeks treatment. Results SBP, DBP and pluse pressure（PP） were markedly decreased（P＜0.01） in metformin group after 24 weeks treatment. At the end of 24 weeks, as metformin group compared with low-fat diet group, SBP were （137±5 vs 142±6）mm Hg, DBP were （88±6 vs 92±4）mm Hg, PP were （40±9 vs 44±8）mm Hg （P＜0.01, P＜0.05）. Conclusion The long-term treatment with metformin can decrease blood pressure in patients with MS.