Therapeutic modalities that overcome the antiapoptotic function of Bcl-2 that is often overexpressed in cancer cells are expected to be a novel strategy for cancer treatment. We previously reported that the leukemic cell death induced by an N-terminally truncated Bax (deltaN Bax: corresponding to amino acid 112-192 of full-length Bax) was not blocked by Bcl-2 or Bcl-x(L) owing to the lack of the BH3 domain needed to interact with the antiapoptotic Bcl-2 family molecules. In this study, we used the Cre-loxP system that allowed us to propagate adenoviruses expressing deltaN Bax, and investigated the effects of the deltaN Bax gene transfer into A549 and NCI-H1299 nonsmall cell lung cancer cell lines. deltaN Bax showed more cell-death-inducing activity in both cells than did the full-length Bax in vitro. It was found that the deltaN Bax-induced cell death was not inhibited by the pan-caspase inhibitor z-VAD-fmk, suggesting that deltaN Bax induces cell death through a caspase-independent mechanism. Intratumoral injection of adenoviruses expressing deltaN Bax into A549 tumors in Balb/c nude mice showed a significantly stronger suppression of tumor growth (74%) than full-length Bax (25%) compared to the control. Our results suggest that deltaN Bax may provide a better alternative than currently used cytotoxic genes in cancer gene therapy trials.