Background: Lung cancer in younger patients seems to be a more aggressive disease and their prognosis may be worse than that of older patients. Abnormal p53 expression in primary lung cancer may be an independent prognostic factor for poor prognosis. This study was conducted to determine the difference of abnormal p53 mutation in patients with primary non-small cell lung cancer (NSCLC) under 45 years of age and 55 years old or greater. Method: The present study was performed to compare the clinical and pathological features of primary NSCLC between patients younger than 45 years old and older than 55 years old and to evaluate the difference of abnormal p53 mutation between two groups. Immunohistochemical detection of abnormal p53 mutation was assessed in all primary NSCLC specimens by pathologist. Results: Positive nuclear staining of p53 mutation was found in 76.0% of younger patients and in 76.9% of older patients with variable intensity of staining. And there was no significant correlation between abnormal p53 mutation according to the disease stage or histologic subtype. Conclusion: In this investigation, these were no difference in p53 mutation between two groups.