The Janus kinase-signal transducers and activators of transcription (JAK-STAT) pathway is one of the most important components of cytokine signaling cascades. JAK-STAT signaling pathway modulates various fundamental biological processes and cancer pathogenesis. JAK-STAT is controlled by negative regulators that include suppressors of cytokine signaling (SOCS) proteins. Failure of feedback suppression by SOCS proteins may result in activated JAK-STAT signaling. Methylation-mediated silencing of SOCS3 has been reported in non-small lung cancer (NSCLC) and other human cancers. In this study, we restored SOCS3 expression using adenovirus-mediated gene transfer in NSCLC cells. Infection with a SOCS3-expressing vector inhibited the growth of lung cancer cells, with or without SOCS3 expression, at 2-3 days after infection. The growth inhibition of lung cancer cells was associated with suppressing entry into the S-phase. Restoration of SOCS3 expression induced apoptosis of NSCLC cells that did not express SOCS3. In addition, overexpression of SOCS3 by adenoviral transfer enhanced the radiosensitivity of treated NSCLC cells. In conclusion, our findings may provide insights into the development of applications of SOCS3 gene therapy for lung cancer and, possibly, other human cancers.