BACKGROUND: Mindfulness-based stress reduction (MBSR) intervention has been widely used to reduce the burden of symptoms in cancer patients, and its effectiveness has been proven. However, the effectiveness of MBSR on depression, anxiety, fatigue, quality of life (QOL), posttraumatic growth (PTG), fear of cancer recurrence (FCR), pain, and sleep in breast cancer patients has not yet been determined. This study aims to determine the role of mindfulness-based stress reduction therapy in patients with breast cancer. OBJECTIVES: The objective was to systematically review the literature to explore the effect of MBSR on anxiety, depression, QOL, PTG, fatigue, FCR, pain, stress and sleep in breast cancer patients. To explore the effect of 8-week versus 6-week MBSR on the 9 indicators. Data were extracted from the original RCT study at the end of the intervention and three months after baseline to explore whether the effects of the intervention were sustained. METHODS: We conducted searches on PubMed, Web of Science, Embase, and China National Knowledge Infrastructure from inception to November 2023. Eligible studies included randomized controlled trials of breast cancer patients who received mindfulness stress reduction intervention, reporting outcomes for anxiety, depression, fatigue, QOL, PTG, FCR, pain, stress, and sleep. Two researchers conducted separate reviews of the abstract and full text, extracted data, and independently evaluated the risk of bias using the Cochrane 'Bias Risk Assessment tool'. The meta-analysis utilized Review Manager 5.4 to conduct the study, and the effect size was determined using the standardized mean difference and its corresponding 95% confidence interval. RESULTS: The final analysis included 15 studies with a total of 1937 patients. At the end of the intervention, the interventions with a duration of eight weeks led to a significant reduction in anxiety [SMD=-0.60, 95% CI (-0.78, -0.43), P < 0.00001, I2 = 31%], depression [SMD=-0.39, 95% CI (-0.59, -0.19), P = 0.0001, I2 = 55%], and QOL [542 participants, SMD = 0.54, 95% CI (0.30, 0.79), P < 0.0001, I2 = 49%], whereas no statistically significant effects were found in the intervention with a duration of six weeks. Similarly, in 3 months after baseline, the interventions with a duration of eight weeks led to a significant reduction in depression and QOL, however, no statistically significant effects were found at the 6-week intervention. MBSR led to a significant improvement in PTG at end of intervention [MD = 6.25, 95% CI (4.26, 8.25), P < 0.00001, I2 = 0%] and PTG 3 months after baseline. We found that MBSR reduced the fatigue status at end of intervention, but had no significant effect on fatigue status 3 months after baseline. There was no significant difference in improving pain, stress, and FCR compared to usual care. CONCLUSIONS: In terms of effects on QOL, anxiety, depression, and fatigue, the 8-week MBSR intervention showed better results than the 6-week MBSR intervention. The intervention of MBSR on PTG was effective, and the effect lasted until 3 months after baseline. Future studies could further identify the most effective intervention components in MBSR. TRIAL REGISTRATION: PROSPERO registration number: CRD42023483980.