Background. As a mind-body exercise, Tai Chi (TC) may have a positive impact on physical function and psychological wellbeing in patients with breast cancer (BC). The aim of this current overview of systematic reviews (SRs) and meta-analyses (MAs) was to identify and summarize the existing evidence regarding the effectiveness of TC in patients with BC. Methods. A computerized search of electronic databases was performed to identify relevant SRs/MAs of TC related to BC from inception to June 2020. The Assessing the Methodological Quality of Systematic Reviews 2 (AMSTAR-2) and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklists were used to assess the methodological quality and reporting quality of SRs and MAs, respectively. The Grades of Recommendations, Assessment, Development and Evaluation (GRADE) approach was used to assess the evidence quality of outcome measures. Results. Six SRs/MAs in which quantitative synthesis was used to assess various outcomes of TC related to BC were included in this overview. The quality of the SRs/MAs and the evidence quality of the outcome measures were generally unsatisfactory. The limitations of the past SRs/MAs were the lack of a protocol and registration, a list of excluded studies, or inadequately reported computational details of meta-analyses. The critical problems were that the qualitative data synthesis relied on the trials with small sample sizes and of critical low quality. Conclusions. TC is possibly beneficial to BC treatment. However, further rigorous and comprehensive studies are required to provide robust evidence for definitive conclusions. J Pain Symptom Manage 2021;61:1052e1059. ? 2020 American Academy of Hospice and Palliative Medicine. Published by Elsevier Inc. All rights reserved.