Non-small cell lung cancer (NSCLC) is a progressive malignant disease, involving the activation of oncogenes and inactivation of tumor suppressors. In this study, we identified and characterized a novel oncogene hematopoietic-and neurologic-expressed sequence 1-like (HN1L) in human NSCLC. Overexpression of HN1L was frequently detected in primary NSCLC compared with their non-tumor counterparts (P < 0.001), which was significantly associated with tumor size (P = 0.022). In addition, Kaplan-Meier analysis showed that upregulation of HN1L correlated with worse overall survival (P = 0.029) and disease-free survival (P = 0.011) for NSCLC patients. Both in vitro and in vivo studies demonstrated that inhibition of HN1L expression with shRNA dramatically inhibited cell growth, adherent and non-adherent colony formation, and tumorigenicity in nude mice. The positive correlation of HN1L expression and Ki67 level in a large NSCLC samples further suggested the key role of HN1L in the regulation of cell growth. Further study showed that knockdown of HN1L resulted in dramatic cell cycle arrest by interfering with MAPK pathway via interacting with RASA4 protein. In conclusion, HN1L plays a crucial role in the progression of NSCLC by contributing to malignant proliferation, with possible use as a new intervention point for therapeutic strategies.