Abstract. Paternally expressed imprinted gene 10 (PEG10), derived from the Ty3/Gypsy family of retrotransposons, has been implicated as a genetic imprinted gene. Accumulating evidence suggests that PEG10 plays an important role in tumor growth in various cancers, including hepatocellular carcinoma, lung cancer and prostate cancer. However, the correlation between PEG10 and breast cancer remains unclear.In the present study, we evaluated and characterized the role of PEG10 in human breast cancer proliferation, cell cycle, clone formation, migration and invasion. The expression level of PEG10 was significantly elevated in breast cancer tissues and associated with distant metastasis and poor clinical outcome. Gene set enrichment analysis indicated that high expression of PEG10 could enrich cell cycle-related processes in breast cancer tissues. Ectopic overexpression of PEG10 in breast cancer cells enhanced cell proliferation, cell cycle, clone formation along with migration and invasion. Cell-to-cell junction molecule E-cadherin was downregulated and matrix degradation proteases MMP-1, MMP-2, MMP-9 were up regulated after PEG10 overexpression. Our results demonstrated that PEG10 is a crucial oncogene and has prognostic value for breast cancer, which could be applied in breast cancer diagnosis and targeting therapy in future.