Objective To explore inhibitory effect of miR-34a on the proliferation of breast cancer cell MCF-7 by targeting Notch1. Methods MCF-7 cells were transferred with miR-34a mimics and miR-34a NC. The expression of miR-34a in MCF-7 cell was examed by RT-PCR. The cell viability was detected by MTT. The cell apoptosis was examed by Hoechst staining. Cell cycle was detected by flow cytometry. Western blot, RT-PCR and dual luciferase reporter gene assay was to detect whether Notch1 was a downstream target gene of miR-34a. Results Compared with miR-34a NC group, the expression of miR-34a was up-regulated, the cell viability was decreased, cell apoptotic rate was increased, cell cycle was arrested in the G1 phase, the expression of Notch1 protein and mRNA was down-regulated (P<0.01). Conclusion miR-34a mimics inhibited MCF-7 cell proliferation and induced cell apoptosis via targeting regulation expression of Notch1.