BACKGROUD: Angiotensin converting enzyme inhibitors (ACEIs) have been linked to reduced risk of new-onset diabetes, but the evidence was insufficient. OBJECTIVE AND METHODS: The aim of this study was to evaluate the effect of ACEIs on the development of new-onset type 2 diabetes. Randomized controlled trials (RCTs) about ACEIs and new-onset diabetes were identified by electronic and manual searches. RESULTS: Nine RCTs with 92,404 patients (72,128 non-diabetic patients at baseline) were included in this study. Compared with control group, incidence of new-onset diabetes was significantly reduced in the ACEIs group [OR 0.80, (0.71, 0.91)], irrespective of achieved blood pressure levels at the follow-up. ACEIs therapy was associated with significant reduction in the risk of new-onset diabetes compared with beta-blockers/diuretics [OR 0.78, (0.65, 0.93)], placebo [OR 0.79, (0.64, 0.96)], or calcium channel blockers [OR 0.85, (0.73, 0.99)]. ACEIs treatment was associated with significant reduction in the risk of new-onset diabetes in patients with hypertension [OR 0.80, (0.68, 0.93)], coronary artery disease (CAD) or cardiovascular disease [OR 0.83, (0.68, 1.00)], or heart failure [OR 0.22, (0.10, 0.47)]. Among patients with impaired glucose tolerance or impaired fasting glucose, ramipril did not significantly reduce the incidence of diabetes [OR 0.91, (0.79, 1.05)], but significantly increased regression to normoglycemia. CONCLUSION: ACEIs have beneficial effects in preventing new-onset diabetes. ACEIs provide additional benefits of lowering the risk of new-onset diabetes in patients with hypertension, CAD or other cardiovascular disease.