Objective To evaluate the effects of mindfulness-based stress reduction(MBSR) on fatigue and sleep quality for breast cancer patients undergoing chemotherapy. Methods Totally 96 patients with breast cancer under-going chemotherapy were assigned into the intervention group and the control group with 48 cases in each group from a tertiary hospital in Zhengzhou city. Both groups received routine care,and the intervention group also received 8 weeks of MBSR. The Revised Piper Fatigue Scale(PFS-R) and Pittsburgh Sleep Quality Index(PSQI) were used to assess fatigue and sleep quality of two groups during chemotherapy before the intervention(T1),after the interven-tion(T2) and 3 months after the intervention (T3). Results There were significant differences in sensory,behav-ioral,emotional and total fatigue scores between the two groups(P<0.05);the time effect on fatigue of the various dimensions scores and total fatigue scores was significant(P<0.05);sensory aspects,emotional aspects,behavioral aspects,and total fatigue scores were interfered between intervention and time factors(P<0.05). There were signifi-cant differences in sleep quality,fall sleep time,sleep time,sleep efficiency and sleep scores between the two groups(P<0.05);the time effect on sleep quality,sleep time, fall sleep time was significant(P<0.05);there were interac-tion effects between intervention and time on sleep quality,sleep time,sleep disturbance and sleep total score(P<0.05). Conclusion MBSR can effectively relieve fatigue and improve sleep quality for breast cancer patients undergoing chemotherapy.