The prognosis in case of non-small cell lung cancer (NSCLC) remains poor, and novel treatment modalities are urgently needed for advanced NSCLC. Backed by advances in the understanding of cancer biology, gene therapy has been developed in recent years. The p53 gene is altered in over 50% of cancers and has been extensively studied as a tumor suppressor gene. Adenoviral-mediated p53 gene transfer is currently under clinical evaluation worldwide for the treatment of cancer. We are now conducting a phase I study of Ad-p53 for advanced NSCLC patients in Japan. As an interim report, we provide a brief summary of the current status of this study, highlighting the safety and clinical efficacy of Ad-p53. As of September 2002, 13 patients were enrolled to this study, and safety and antitumor effects have been noted.