BACKGROUND & AIMS: Results from randomized controlled trials (RCT) of B vitamin supplementation on risk of cardiovascular disease (CVD) were inconclusive. The aim of the present study was to systematically review the effects of B vitamin supplementation on plasma homocysteine (Hcy), cardiovascular and all-cause mortality in RCT. METHODS: RCT publications on the effect of B vitamin supplementation on plasma Hcy, cardiovascular and all-cause mortality were searched from PubMed and web of science database. Data were independently abstracted by 2 investigators using a standardized protocol. The results were pooled with a fixed-effects model using Stata software. RESULTS: Data from 19 studies including 47921 participants were analyzed using a fixed-effects model. The overall relative risks with 95% confidence intervals of outcomes for patients treated with B vitamin supplementation compared with placebo were 0.98 (0.94-1.03) for CVD, 0.98 (0.92-1.05) for coronary heart disease (CHD), 0.97 (0.90-1.05) for myocardial infarction (MI), 0.88 (0.82-0.95) for stroke, and 0.97 (0.91-1.02) for cardiovascular death, 0.99 (0.95-1.04) for all-cause mortality. Blood Hcy levels were decreased in all included RCTs. CONCLUSIONS: B vitamin supplementation has a significant protective effect on stroke, but none on the risk of CVD, MI, CHD, cardiovascular death, or all-cause mortality.