Background Dietary branched chain amino acids (BCAAs) are proposed as a potential related factor in various diseases, including cancer. We aimed to investigate the relationship between dietary intake of BCAAs and their components with cancer and all-cause mortality in a meta-analysis study of observational studies. Methods To identify relevant studies, a comprehensive search was conducted between electronic databases (PubMed, Scopus, and Web of Science) until September 2022. Odds ratios (OR), hazard ratios (HR), and relative risks (RR) with 95% confidence interval (CI) were extracted from eligible studies, and a meta-analysis was performed to calculate the combined effect size. Results Eight articles (3 case-control and 5 cohorts) were included in this meta-analysis. 6 studies reported effect sizes for cancer risk and 3 for cancer or all-cause mortality. Overall, we did not observe any statistically significant association between dietary intake of BCAAs and their components with cancer (RRBCAA: 0.87, 95%CI: 0.68–1.10, RRLeucine: 0.74, 95%CI: 0.52–1.04, RRIsoleucine: 0.98, 95%CI: 0.93–1.04, RRValine: 0.76, 95%CI: 0.55–1.05). Also, we observed any significant relationship between dietary BCAAs and their components with both cancer mortality (RRBCAA: 0.95, 95%CI: 0.68–1.33, RRLeucine: 0.95, 95%CI: 0.79–1.15, RRIsoleucine: 0.95, 95%CI: 0.79–1.14, RRValine: 1.01, 95%CI: 0.84–1.21) and all-cause mortality (RRBCAA: 0.98, 95%CI: 0.73–1.32, RRLeucine: 1.02, 95%CI: 0.81–1.29, RRIsoleucine: 0.96, 95%CI: 0.73–1.27, RRValine: 1.02, 95% CI: 0.79–1.32). Conclusions The findings of the present study showed no significant association between dietary intake of BCAA and its components with cancer, cancer mortality, and all-cause mortality.