microRNAs (miRNAs) have emerged as major regulators of the initiation and progression of human cancers， including breast cancer. The aim of this study is to determine the expression pattern of miR-96 in breast cancer and to investigate its biological role during tumorigenesis. We showed that miR-96 was significantly upregulated in breast cancer. We then investigated its function and found that miR-96 significantly promoted cell proliferation， migration and invasion in vitro and enhanced tumor growth in vivo. Furthermore， we explored the molecular mechanisms by which miR-96 contributes to breast cancer progression and identified PTPN9 (protein tyrosine phosphatase， non-receptor type 9) as a direct target gene of miR-96. Finally， we showed that PTPN9 had opposite effects to those of miR-96 on breast cancer cells， suggesting that miR-96 may promote breast tumorigenesis by silencing PTPN9. Taken together， this study highlights an important role for miR-96 in the regulation of PTPN9 in breast cancer cells and may provide insight into the molecular mechanisms of breast carcinogenesis.