Background: Maspin (mammary serine protease inhibitor) is a member of the serpin superfamily. A few studies have examined the role of maspin in tumor suppression of non-small cell lung cancer (NSCLC); however, its role in the development and progression of NSCLC still remains controversial. We evaluated the immunohistochemical expression of maspin in order to elucidate its clinical significance in NSCLC. Methods: We analyzed 145 patients with pathologically confirmed NSCLC, including 66 cases of squamous cell carcinomas (SCCs) and 79 cases of adenocarcinomas (ADCs). We performed a immuno-histochemical stain with maspin and PCNA (proliferating cell nuclear antigen) using tissue microarray blocks. Results: There were 108 men and 37 women in the study population. The mean age of patients in the study was 63.7 years (range, 40.0~82.0; median, 65.0). The proportion of maspin expression was significantly higher in SCCs (52/66, 78.8%; p<0.01) than in ADCs (17/79, 21.5%; p<0.01). Maspin expression was not associated with PCNA (p=0.828), lymph node involvement (p=0.483), or tumor stage (p=0.216), but showed correlation with well-to-moderate tumor differentiation (p=0.012). There was no observed correlation between maspin expression and survival with NSCLC (p=0.218). Conclusion: The present study suggests that maspin expression was significantly higher in SCCs than in ADCs and was associated with low histological grade. However, maspin expression was not an independent factor to predict a prognosis in NSCLC.