OBJECTIVE: Orthodenticle Homeobox 1 (OTX1) has been found to be closely related to the development of several human tumours. However, the function and underlying molecular mechanisms of OTX1 in non-small cell lung cancer (NSCLC) are unclear. This research was performed to investigate the effects of downregulating OTX1 gene expression on the proliferation, migration, invasion, cell cycle and apoptosis of human NSCLC cell lines. PATIENTS AND METHODS: Cultured NCI-H292 and XWLC cells were transfected with control small interfering RNA (siNC) or experimental siRNA (siOTX1). The mRNA levels were detected using a quantitative real-time PCR (RT-qPCR) assay. A Cell Counting Kit-8 (CCK-8) and a Real Time Cell Analyzer (RTCA) were used to determine cell activity. The RTCA and transwell chambers were used to assess cell migration and invasion. In addition, cell cycle progression and apoptosis were measured using flow cytometry, and the expression levels of key signalling pathway proteins were examined by Western blotting. RESULTS: The results revealed that compared with the control group, the experimental group exhibited significantly decreased cell activity (***p<0.001), significantly decreased migration and invasion abilities (***p<0.001), and cell cycle arrest in G2/M phase (*p<0.05). However, the number of apoptotic cells was higher in the experimental group than in the control group (*p<0.05). The Western blotting results were consistent with the functional experiment results. CONCLUSIONS: Silencing the OTX1 gene suppressed the proliferation, migration and invasion of NCI-H292 and XWLC cells, impeded the cell cycle transition from G2 to M phase, and accelerated apoptosis, revealing OTX1, a regulator of NSCLC, as a potential new therapeutic target.