MicroRNAs (miRNAs) have important roles in the initiation and progression of human cancer, including breast cancer. We evaluated miR-365 expression in breast cancer tissues, and investigated its effects on cell growth, cell cycle, cell invasion, and expression of its target gene ADAMTS-1. miR-365 expression levels were analyzed in breast cancer tissues and adjacent normal tissues using qRT-PCR. CCK-8, cell cycle, and invasion assays were used to explore the role of miR-365 expression in breast cancer cells. We conducted luciferase reporter and western blot assays to test whether ADAMTS-1 is a direct target of miR-365. We found that miR-365 expression levels were significantly higher in breast cancer tissues compared with adjacent non-tumor tissues (P<0.05). These relatively high expression levels were significantly associated with advanced clinical stages (P<0.05). In breast cancer cell lines, transfection with miR-365 inhibitor suppressed proliferation and invasion, and resulted in cell cycle arrest. Subsequent experiments indicated that miR-365 bound the 3′-UTR of ADAMTS-1 and downregulated its expression. Our findings indicated that the inhibition of miR-365 reduced cell proliferation and cell invasion. Additionally, miR-365 may function as a novel oncogene in breast cancer through targeting ADAMTS-1. These findings provide insight into the mechanism of breast cancer pathogenesis.