Objective To investigate the expression and the clinical significance of Livin and Caspase-9 protein in squamous cell carcinoma tissue.Methods Livin and Caspase-9 protein expression was detected in 56 SCC and 20 normal skin specimens by SP immunohistochemical technique.Results The positive expression rate of Livin protein in SCC ( 73.2% ) was higher than that in normal lung tissue (0.0% ).There was significant difference in the positive expression rate of Livin between squamous cell carcinoma and normal skin tissues (P <0.05).The expression of Livin protein was correlated with the differentiation of squamous cell carcinoma and the positive expression rate of Livin protein was increased in squamous cell carcinoma from high differentiation to poor differentiation with a statistically significant difference (P<0.05).The positive expression rate of Livin protein in SCC tissue was related with lymph node metastasis ( P < 0.05 ).Caspase-9 protein showed lower expression in SCC ( 30.4% ) than in normallung tissue (90.0% ) (P <0.05).The expression of Caspase-9 is correlated with the differentiation of squamous cell carcinoma.The positive expression rate of Caspase-9 was decreased in squamous cell carcinoma from high differentiation to poor differentiation with a statistically significant difference ( P < 0.05 ).The positive expression rate of Caspase-9 protein in SCC tissue was related with lymph node metastasis ( P <0.05 ).The expression of Livin protein was negatively related to that of Caspase-9 protein in SCC tissues (rs =-0.612,P < 0.05 ).Conclusion The expression of Livin protein in SCC was high,while the positive expression of Caspase-9 protein in SCC was lower,and there was a negative correlation between them,and both Livin and Caspase-9 may play important roles in the carcinogenesis of SCC together,which may provide the new ideas for the clinical diagnosis,treatment and prognosis judgement of SCC. Key words: Livin; Caspase-9; Squamous cell carcinoma; Immunohistochemistry