Abstract: Objective: To explore the relationship between p33 ^ING1b expression and clinicopatholog-ic characteristics in non-small cell lung carcinoma (NSCLC) and the possible mechanism of p33 ^ING1b in the oncogenesis of NSCLC. Methods: Immunohistochemistry staining (labeled streptavidin-biotin method) were used to detect p33 ^ING1b expression in NSCLC and non-neoplasia lung tissues and p21 ^WAF1and Bax in NSCLC. Results: The positive rate of p33 ^ING1b in 61 cases of NSCLC was significantly lowerthan those in non-tumorous lung tissues, P<0.01. The down-regulation of the expression of p33 ^ING1b wasrelated to differentiation and TNM stages, as well as to lymph-node metastases. The positive rate of p33 ^ING1b in poorly differentiated group was significantly lower than those in well and moderately-differ-entiated group, P<0.05. The positive rates of p33 ^ING1b in stage and lymph node metastases groups weresignificantly lower than those in stage + and the groups without lymph node metastasis, P<0.01. The ex-pression of p21^WAF1 was positively correlated with the expression of p33 ^ING1b, P<0.01. Conclusion: 1) The expression of p33 ^ING1b is reduced in NSCLC. The down-expression of p33 ^ING1b is useful for evaluating the malignancy level, invasion and metastasis of NSCLC; 2) The down- expression of p33 ^ING1b might allow thedown-regulation of p21 ^WAF1 to play an important role in the oncogenesis of NSCLC.