Abstract: Objective To investigate the effects of cyclosporine A on the proliferation and pol α1 mRNA expression of cultured NIT-1 β cells.Methods After exposure to cyclosporine A at various concentrations (0.05 to 10 μmol/L) for 48 h and 72 h, NIT-1 cell proliferation was analyzed by MTT assay and the gene expression determined by reverse transcriptional PCR (RT-PCR).Results Forty-eight-hour and 72-hour cyclosporine A exposure inhibited the cell proliferation in a concentration- dependent manner, and at the concentration of 10 μmol/L, cyclosporine A also decreased pol α1 mRNA expression after a 48-hour exposure.Conclusion Cyclosporine A can effectively inhibit the proliferation of NIT-1 cells possibly through down-regulating the expression of pol α1 mRNA.