We conducted a study on the mechanism of KAI1/CD82-mediated suppression of tumor invasiveness and metastasis, and examined its effect on MMP-9 activity and the TIMP1 levels in H1299 human non-small cell lung carcinoma cells. The H1299 human lung carcinoma cells were transfected with pcDNA3.1-CD82 and stable transfectant clones that had a high KAI1/CD82 expression were obtained. We performed Western blot analysis, cell invasion assay, gelatin zymography, and RT-PCR to assess the KAI1/CD82 expression and tumor invasiveness, the MMP-9 activity, the MMP-9 mRNA and protein levels, and the TIMP1 levels in the H1299/CD82 transfectant cells and compared the results with those of the control groups. The H1299/CD82 transfectants exhibited significant suppression of cell invasion, reduced MMP9 enzyme activity, elevated MMP9 mRNA and MMP-9 protein levels, and elevated TIMP1 levels. It may be postulated that KAI1/CD82 over-expression in the H1299 non-small cell lung carcinoma cells suppresses the tumor invasiveness and metastatic potential by inducing MMP9 inactivation via the up-regulation of TIMP1.