Recent evidence highlights that microRNAs serve as crucial regulators of tumorigenesis, including non-small cell lung cancer (NSCLC). The present study was designed to investigate the expression profile, clinical significance and biological role of miR-421 in NSCLC. The results showed that miR-421 expression was markedly increased in NSCLC tissues and cell lines. Further experimental data indicated that knockdown of miR-421 significantly inhibited NSCLC cell proliferation and induced cell cycle arrest in vitro. The migratory and invasive abilities of NSCLC cells were also attenuated following miR-421 knockdown. Furthermore, PDCD4 was identified as a direct target of miR-421, and its expression was inversely correlated with miR-421 expression in NSCLC tissues. PDCD4 also abrogated the oncogenic role of miR-421 in NSCLC cells. Collectively, our study revealed that miR-421 is significantly upregulated in NSCLC and might represent a potential therapeutic target for NSCLC patients.