Abstract: Objective: To study the relationship between INK4a/ARF genes methylation and proteins co-expression in non-small cell lung cancer. Methods: Sections were obtained from previous 10%-formalin-fixed and paraffin-embedded tissues, including 35 NSCLC samples with p14^ARF and p16^INK4a negative co-expression and 20 NSCLC samples with p14^ARF and p16^INK4a positive co-expression. These samples were divided into two groups and were named as the (p14+p16) negative group and the (p14+p16) positive group respectively. The 5'CpG islands methylation state of tumor suppressor gene INK4a/ARF was determined by methylation specific polymerase chain reaction (MSP). Results: The hypermethylation rate of INK4a gene was 51.4 %(18/35) in (p14+p16) negative group, but 10 %(2/20) in (p14+p16) positive group. There was a significant difference between the two groups (P=0.002). The hypermethylation frequency of ARF gene was 22.8 %(8/35) in the (p14+p16) negative group, and was 10 %(2/20) in the (p14+p16) positive group. There was no significant difference between the two groups(P=0.409) and was no obviously correlation between INK4a gene hypermethylation and ARF gene hypermethylation. Conclusion: INK4a gene hypermethylation is one of the important mechanisms that results in p16^INK4a proteins negative expression in NSCLC. The hypermethylation of INK4a and ARF genes are independent each other.