Abstract: Objective To investigate the role of miR- 433 in chemoresistance to docetaxel in breast cancer cells. Methods A docetaxel-resistant MCF-7 breast cancer cell line (MCF-7/DOX) was established by exposure of parental MCF-7 cells to progressively increased docetaxel concentrations. The functional role of miR-433 was investigated by assessing the changes in viability and apoptosis of the cells transfected with a miR-433 inhibitor or a miR-433 mimics. The downstream targets of miR- 433 were determined by bioinformatics analysis, cell transfection and luciferase reporter assay. Results Quantitative real-time PCR analysis showed that miR- 433 was down-regulated in MCF-7/DOX cells. Transfection of the cells with the miR-433 inhibitor obviously enhanced chemoresistance to docetaxel and attenuated cell apoptosis in MCF-7 cells; miR-433 overexpression significantly increased the sensitivity to docetaxel and promoted apoptosis in MCF- 7/DOX cells. Luciferase reporter assay showed that the down-regulation miR-433 expression was associated with significantly increased expressions of Notch1 at both mRNA and protein levels in MCF-7 cells. Compared with the control cells, McF-7/DOX cells transfected with miR-433 mimics exhibited significantly decreased mRNA and protein expressions of Notch1. Conclusions miR-433 may reverse chemoresistance to docetaxel by targeting Notch1 in breast cancer cells.