Abstract: Objective: To investigate the effect of stable transfection of the exogenous wild KAI1 gene on biological behavior of the breast cancer cell in vitro. Methods: Human breast cancer cell lines MDA-MB-231 was transfected with pCMV-KAI1 or mock transfected plasmid pCMV with lipofectamine. Western blot was used to determine the expression of target protein of KAI1. The proliferative ability of cells was tested by MTT assay and the metastatic ability was investigated by cell adhesion and invasion assay. The contents of ICAM-1 before and after the transfection were also measured using ELISA assay. Results: The MDA-MB-231 breast cancer cell clone with stable expression of KAI1 gene was acquired and a high expression of the KAI1 protein was observed. The MTT showed cell proliferation ability was lower in the transfection group than in the non-transfection and mock-vehicle groups (P<0.05). Experiments on the in vitro adherency and invasiveness showed that cell adhesion and invasion ability was lower in the transfection group compared to that in the non-transfection and mock-vehicle groups (P<0.05). The content of sICAM-1 decreased after the transfection. Conclusion: The KAI1 gene can restrain malignant phenotypes of the human breast cancer cells in vitro and may inhibit the metastasis by influencing the function of some adherence factors.