[Abstract] Objective： ： To explore miR-103a-3p expression in the tumor tissues and the serum of breast cancer patients, and its role and mechanism in breast cancer development. Methods: Pathologically confirmed 31 cases of tumor tissues and 21 cases of para-cancerous tissues resected at Department of Oncological Surgery of the Second Affiliated Hospital of Hainan Medical University (Haikou, China) from March 1, 2017 to August 31，2017 were collected for this study; in addition, serum samples from 38 breast cancer patients and 22 healthy subjects as well as the breast cancer cell lines MCF-7 and MDA-MB-231 were used in this study. pHBLV-U6-Luc-T2A-Puro and PLL3.7 lentivirus were applied to knock down miR-103a-3p and PDK4 in MCF-7 and MDA-MB-231 cells, respectively. qPCR and Western blotting were performed to examine the mRNA and protein expressions of miR-103a-3p and PDK4 in tissues and serums of breast cancer patients as well as the in cell lines, respectively; CCK-8 assay was applied to detect the proliferation of MCF-7 and MDAMB-231 cells; Olympus AU5400 was applied to detect the glucose consumption and lactate production in indicated cell line. Results： ： miR-103a-3p was significantly decreased in tumor tissues compared with the paracancerous tissues (P<0.01). miR-103a-3p knockdown activated the glucos consumption and lactate production (all P<0.01), increased the PKD4 expression (P<0.01) in MCF-7 and MDAMD-231 cells, and promoted the proliferation of MCF-7 and MDA-MB-231 cells (P<0.01). Furthermore, knockdown of PDK4 suppressed the glucose consumption, lactate production and proliferation in MCF-7 and MDA-MB-231 cells with miR-103a-3p silencing (all P<0.01). Conclusion： ：In the breast cancer, miR-103a-3p inhibited the proliferation of breast cancer cells through down-regulation of PDK4 and PDK4-mediated aerobic glycolysis.