Lung cancer is the primary cause of cancer‑associated mortality in men and women worldwide. Increasing evidence indicates that abnormal microRNA (miRNA) expression contributes to the carcinogenesis and progression of multiple human cancers, including non‑small cell lung cancer (NSCLC). Therefore, miRNAs exhibit the potential to act as biomarkers for the diagnosis, treatment and prognosis of human malignancies. miRNA‑661 (miR‑661) has previously been demonstrated to be important in the development of various human cancer types. However, the expression levels, functions and underlying mechanisms of miR‑661 in NSCLC remain to be elucidated. The present study demonstrated that miR‑661 was upregulated in NSCLC tissues and cell lines. In addition, miR‑661 expression levels were significantly correlated with differentiation and tumor stage lymph node metastasis of NSCLC patients. Functional experiments demonstrated that miR-661 downregulation inhibited NSCLC cell proliferation and invasion in vitro. Furthermore, runt‑related transcription factor 3 (RUNX3) was identified as a direct target of miR‑661 in NSCLC. RUNX3 was expressed at a low level in NSCLC tissues and was negatively correlated with the miR‑661 expression level. Further experiments revealed that RUNX3 knockdown significantly rescued the effects of miR‑661 underexpression on NSCLC cell proliferation and invasion. In conclusion, the present findings indicated a role for miR‑661 as an oncogene in NSCLC via direct targeting of RUNX3, thus suggesting that miR‑661 may be used to develop novel therapies for NSCLC patients.