Objective To evaluate microsatellite instability(MSI) and loss of heterozygosity(LOH) of the repetitive untranslated 5’region of the nm23H1 gene and their influence on the expression of nm23H1 in Chinese with squamous cell lung carcinoma(SLC). Methods Techniques such as DNA extraction from tissue and fluorescencebased polymerase chain reaction singlestrand conformation polymorphism(FPCR-SSCP) combined with an automated DNA sequencer were used to study MSI and LOH of nm23H1. Immunohistochemistry and LeicaQwin computer imaging techniques were used to assess the expression of nm23H1 gene. Results Of these cases of informative tumors 44 of 50, the frequencies of MSI, LOH and nm23 H1 protein positive were 11.36%, 25.00% and 50.00% respectively. The frequencies of MSI were 8.70%， 10.00% and 18.18% in TNM stage Ⅰ, Ⅱ and Ⅲ respectively; The frequencies of LOH were 30.43%, 20.00% and 18.18% in TNM stage, Ⅰ, Ⅱ and Ⅲ respectively and the frequency of MSI and LOH were 10.00% and 20.00% in lymph node metastasis cases compared with 12.50% and 29.17% in those without metastasis. However, the frequencies of MSI and LOH showed no correlation with TNM stage and lymph node metastasis(P>0.05). All the 5 cases with MSI positive belonged to moderate (G2) or good(G1) histological grade and all were alive in a year, but the frequency of MSI was not related to tumor differentiation and survival status of patient(P>0.05). The positive frequency of nm23H1 protein in lymph node metastasis cases (30.00%) was significantly lower than those without metastasis(66.67%)(P<0.05). TNM stage Ⅲ(18.18%) also exhibited lower positive frequency of nm23H1 protein compared with stage Ⅰ(65.22%)(P<0.05). Furthermore, the frequencies of MSI and LOH were not related to the expression of nm23H1 protein(P>0.05). There was also no difference in nm23H1 protein expression intensity analyzed by computer imaging(P>0.05). Conclusion The increase in the amount of nm23H1 protein expression can play an important role in restraining metastasis of squa