S100 proteins, a family of Ca(2+)-binding proteins, have been linked to several human diseases in recent years. Deregulated expression of S100 proteins, including S100A9 and its partner S100A8, was reported to be associated with neoplastic disorders. In our previous study using serial analysis of gene expression, we identified decreased expressions of S100A9 and S100A8 in human cervical squamous cell carcinoma. To investigate the functions of S100A8 and S100A9 in cervical cancer, we purified recombinant S100A8 and S100A9 proteins and treated CaSki human cervical cancer cells with these proteins. We found that S100A8/A9 induced apoptosis and inhibited migration of CaSki cells; S100A8/A9 also reduced the expression of matrix metalloproteinase (MMP)-2 in CaSki cells. In summary, this study suggests that S100A8 and S100A9 have inhibitory effects on the proliferation of CaSki carcinoma cells by inducing cell apoptosis and on the invasiveness of CaSki cells.