Hexokinase 2 (HK2) has been identified as an oncogene in some malignant diseases such as breast cancer and ovarian cancer. However, the role of HK2 in lung cancer remains unclear. In this study, we explored the functional role of HK2 in lung cancer cell proliferation and tumorigenesis and determine its expression profile in lung cancer. HK2 expression was increased in primary lung cancer tissues of patients. Knocking down HK2 expression by small interfering RNA (siRNA) inhibited cell proliferation in lung cancer cells and nude mice. Thus, HK2 is required for sustained proliferation and survival of tumor cells in vitro and in vivo, and its aberrant expression may contribute to the pathogenesis of lung cancer. Thus, our study provided evidence that HK2 functions as a novel oncogene in lung cancer and may be a potential therapeutic target for lung cancer.