Abstract: OBJECTIVE To investigate the effect and mechanism of miR-489 on enhancing the anti-tumor effect of carboplatin on breast cancer. METHODS Cell viability of T-47D which were treated with miR-489 and carboplatin was measured by using MTT assay. Bioinformatics, western blot analysis and luciferase reporter assay were performed to confirm whether the XIAP was the target of miR-489. After removal of mitochondria, western blot analysis was conducted to detect the release of Smac/DIABLO and activation of caspase-9 and caspase-3 in T-47D cells treated with carboplatin and miR-489. Co-immunoprecipitation assay was performed to evaluate the interaction with XIAP and Smac/DIABLO. Flow cytometry analysis was used to measure the cell apoptosis of T-47D. RESULTS Results of MTT assays showed that miR-489 significantly enhanced the cytotoxicity of carboplatin to T-47D. Results of bioinformatics, western blot analysis and luciferase reporter assay showed that XIAP was the target of miR-489 in T-47D. Overexpression of miR-489 couldn't influence the carboplatin-induced release of Smac/DIABLO. However, miR-489 was able to inhibit the interaction of Smac/DIABLO and XIAP through down-regulating the expression of XIAP in T-47D. In addition, transfection with XIAP plasmid significantly abolished the synergistic effect of miR-489 on carboplatin-induced cytotoxicity to breast cancer. Results of flow cytometry showed that transfection with XIAP plasmid significantly abolished the miR-489-promoed apoptosis induced by carboplatin. Results of Western blot analysis showed that transfection with XIAP plasmid significantly abolished the miR-489-promoed activation of caspase-9 and caspase-3 induced by carboplatin. CONCLUSION MiR-489 targets XIAP to enhance the anti-tumor effect of carboplatin on breast cancer.