A number of epidemiologic studies have attempted to link the use of β blockers to mortality in cancer patients, but their findings have been inconclusive. A meta-analysis was carried out to derive a more precise estimation. Relevant studies were identified by searching PubMed and EMBASE to May 2015. We calculated the summary hazard ratios (HRs) and 95% confidence intervals (CIs) using random-effects models. Twenty cohort studies and four case–control studies involving 76 538 participants were included. The overall results showed that patients who used β blockers after diagnosis had an HR of 0.89 (95% CI 0.81–0.98) for all-cause mortality compared with nonusers. Those who used β blockers after diagnosis (vs. nonusers) had an HR of 0.89 (95% CI 0.79–0.99) for cancer-specific mortality. Prediagnostic use of β blockers showed no beneficial effect on all-cause mortality or cancer-specific mortality. Stratifying by cancer type, only breast cancer patients who used β blockers after diagnosis had a prolonged overall survival. A linear but nonsignificant trend was found between postdiagnostic β-blocker use and mortality of cancer patients. In conclusion, the average effect of β-blocker use after diagnosis but not before diagnosis is beneficial for the survival of cancer patients.