Background: Chemotherapy followed by endocrine therapy is the standard adjuvant treatment strategy for estrogen receptor-positive breast cancer patients. However, no direct evidence so far demonstrated better efficacy of sequential use of chemotherapy and endocrine therapy over concurrent. Objective: To evaluate the efficacy between sequential and concurrent use of chemotherapy and endocrine therapy in the adjuvant treatment of ER positive breast cancer. Methods: Randomized clinical trials comparing chemotherapy and/or endocrine therapy in the adjuvant treatment of ER positive breast cancer were included. Hazard ratios (HRs) of disease-free survival (DFS) and overall survival (OS) were extracted and analyzed in Bayesian analysis. Patients were stratified by menopause status for subgroup analysis. Results: 37 trials were identified with 37225 patients enrolled in total, 37 trials with DFS results and 24 with OS. 3 comparisons were done between sequential and concurrent arms. In DFS analysis, no statistical significance was found in all 3 comparisons [CHE seq/con TAM (HR 1.01, 95%CI 0.8497 - 1.199); CHE seq/con OFS+TAM (HR 0.9119, 95%CI 0.5666 - 1.49); CHE seq/con OFS+AI (HR 1.032, 95%CI 0.6291 - 1.776)]. The same were seen in OS analysis [CHE seq/con TAM (HR 0.9512, 95%CI 0.8053 - 1.125); CHE seq/con OFS+TAM (HR 1.065, 95%CI 0.6344 - 1.789); CHE seq/con OFS+AI (HR 1.069, 95%CI 0.665 - 1.717)]. Rankings were done for preferable treatment recommendations. In DFS analyses, sequential arms ranked higher than concurrent arms [CHE seq/con OFS+AI (1 vs. 3); CHE seq/con OFS+TAM (6 vs. 7); CHE seq/con TAM (8 vs. 8)]. The same tendency was seen in OS analyses [CHE seq/con OFS+AI (1 vs. 2); CHE seq/con TAM (4 vs. 5)] except for CHE seq/con OFS+TAM (11 vs. 6-9). In subgroup ranking results, CHE seq/con OFS+AI and CHE seq/con OFS+TAM showed consistency among comparisons with concurrent arms ranked higher than sequential arms. However, CHE seq TAM ranked higher than CHE con TAM in all comparisons. Conclusions: The combination of chemotherapy and endocrine therapy in the adjuvant treatment of ER positive breast cancer demonstrated equal efficacy either used sequentially or concurrently. However, concurrent arms were recommended over sequential arms in premenopausal patients for better DFS and OS, except for the combination of chemotherapy and tamoxifen which was recommended to be used sequentially. Others: This study has been registered in PROSPERO (CRD42018104889).