Abstract: Objective To investigate the changes of pancreatic β cell function and evaluate the effect of ramipril on the function of β cell in patients with essential hypertension（EH）. Methods Proinsulin（PI）, true insulin（TI） and immunoreactive insulin（IRI） were measured in 44 cases of EH and 21 cases of EH before and after ramipril trentment, 24 normal subjects served as control. Results PI（17.2±8.2 vs 7.9±2.8 pmol/L） and IRI（21.0±12.4 vs 14±7.8μU/ml） in EH were significantly higher than that of control group（ P＜ 0 01, P＜ 0 05）,with no differences in TI（8.4±4.0 vs 7.4±2.4μU/ml） （ P＞ 0 05）.The function index of pancreatic β cell （0 81±0 32 vs 0 56±0 17） increased significantly（ P＜ 0 01）. Plasma concentration of IRI（21.9±5.1 vs 14.9±4.1 μU/ml ）,PI（19.3±8.0 vs 12.5±8.2 pmol/L） （ P＜ 0 05, P＜ 0 01）, and PI/IRI（0 78±0 31 vs 0 54±0 16） decreased markedly （ P＜ 0 01）. ISI（-4.4±0 6 vs -3.5±0 2） increased significantly （ P＜ 0 01）. The level of TI（7.2±3.8 vs 8.2±4.2μU/ml） remained unchanged. Conclusion The plasma concentration of PI and IRI were higher in EH than in control,that indicating EH had remarkable hyperproinsulinemia. Ramipril decreased the level of PI and IRI,improved the function of pancreatic β cell and increased insulin sensitivity. The antihypertensive effect of ramipril may be partially ascribed to its improving of pancreatic β cell function.