Objective: This study aims to evaluate the treatment effect of a mindfulness-based intervention for Chinese breast cancer patients across outcome domains, including symptom-related, psychosocial, and quality of life outcomes. Methods: Following the Cochrane Systematic Review guideline, we searched across five electronic databases, reference lists of eligible studies, professional websites, and major academic journals in Chinese. Publication bias was assessed using funnel plot and Vevea and Woods sensitivity analysis, and risk of bias was evaluated using the revised Cochrane risk of bias tool for randomized trials and risk of bias in non-randomized studies of interventions. A meta-analysis of Hedges’ g was conducted using meta-regression with robust variance estimation. Results: Final analysis included a total of 45 controlled trials containing 286 effect size estimates. Across outcome domains, studies reported an overall large and statistically significant treatment effect, d = 0.921, 95% CI (0.805, 1.040), p < 0.001. Subgroup analyses of specific domains of outcome reported overall significant treatment effects for (1) symptom-related outcomes, d = 0.885, 95% CI (0.657, 1.110), p < 0.001; (2) psychosocial wellness outcomes, d = 0.984, 95% CI (0.879, 1.090), p < 0.001; and (3) quality of life, d = 0.990, 95% CI (0.776, 1.200), p < 0.001. Moderator analysis did not identify any significant moderator. Conclusion: Chinese literature reported an overall statistically significant and large treatment effect of a mindfulness-based intervention for breast cancer patients in China. Except for physical symptom outcomes, e.g., nausea/vomiting and pain, a mindfulness-based intervention was effective across outcome domains among Chinese breast cancer patients.