Objective: To investigate the influence of anti-keratin autoantibodies (AK auto Abs) on telomerase activity of squamous cell carcinoma cultured in vitro and the mechanisms of the inhibitory effects of AK auto Abs on squamous cell carcinoma. Methods: Influence of AK auto Abs on the proliferation of Tca cells was observed by MTT colorimetry. Telomerase activity of cultured Tca cells and human keratinocytes was determined by telomeric repeat amplication protocol-ELISA (TRAP-ELISA) and polyacrylamide gel electrophoresis (PAGE). After being treated with AK auto Abs for 36 h at a concentration of 4, 8, 16 mg/L respectively, the changes of telomerase activity of Tca cells were also detected by TRAP-ELISA and PAGE.Results: MTT colorimetric determination showed that the capacity of proliferation of Tca cells correlated negatively with the concentration of AK auto Abs (r=-0. 74, P＜0. 01). TRAP-ELISA and PAGE showed that telomerase activity of Tca cells increased significantly compared to that of cultured human keratinocytes(t=3. 5396, P＜0. 01). AK auto Abs at a concentrations of 4, 8, 16 mg/L had significant dose-dependent inhibitory effects on telomerase activity of Tca cells (r=- 0. 8358, P＜0. 01). Conclusion: AK auto Abs have a significant dose-dependent inhibitory effect on the proliferation of cultured Tca cells. AK auto Abs inhibit telomerase activity of cultured Tca cells with dose-dependent patt. It suggests that decrease of telomerase activity may play an important role in the inhibitory effects of AK auto Aba on squamous cell carcinoma.