The over-expression of urokinase receptor in breast cancer cells results in increased tumor invasion, growth and metastasis. As LY-6K belongs to the Ly6/uPAR superfamily, we assessed the association of LY-6K with metastasis in breast cancer cell lines and how the LY-6K gene mediates cancer cell metastasis. The migration ability of cells in which expression of LY-6K gene is up- or down-regulated was investigated by transfecting LY-6K naked DNA and treating LY-6K siRNA. Assays of wound healing, migration and invasion were performed. The assays demonstrated that cell migration significantly increased when LY-6K gene is over-expressed or LY-6K protein is abnormally expressed in breast cancer cells. In addition, LY-6K caused cancer cell metastasis and it is linked to the Ras/ERK signaling pathway. Our results suggest that LY-6K meaningfully participates in breast cancer cell metastasis by influencing cell migration and invasion through the Ras/ERK pathway.