MicroRNAs (miRNAs) play a critical role in cancer development and progression. Aberrant expression of miR-15a has recently been reported in several cancers, but its role in non-small cell lung cancer (NSCLC) still remains obscure. We investigated the effects of miR-15a on proliferation, apoptosis, and metastasis in A549 cells. Eighteen paired NSCLC and adjacent non-tumor lung tissues were surgically removed and immediately snap frozen until total RNA was extracted and confirmed by two independent pathologists. The targets of miR-15a were predicted by bioinformatics tools. RNA isolation and quantitative real-time PCR (qRT-PCR), Western blot analysis, cell proliferation assay, cell cycle analysis, cell apoptosis assay, and migration and invasion assays were done. The wild type (WT) or mutant type (MT) 3′-untranslated region (UTR) vectors were co-transfected with miR-15a or negative control into A549 cells, and after 24 h of transfection, luciferase activity was measured using the Dual-Glo luciferase assay kit. Statistical analysis was performed using SPSS 13.0 software (SPSS, Chicago, IL, USA). P values of less than 0.05 were considered statistically significant. miR-15a was significantly downregulated in NSCLC than in adjacent non-cancerous tissues. miR-15a overexpression remarkably inhibited cell viability, invasion, and migration and promoted the apoptosis of NSCLC cells. Additionally, inhibition of miR-15a expression had the opposite effects on tumor progression, while cell cycle remained unaltered. Furthermore, we identified that BCL2L2 was a target of miR-15a and negatively regulated by miR-15a at the translational level. miR-15a acts as a tumor suppressor in NSCLC by directly targeting BCL2L2 and may serve as a potential diagnostic biomarker and therapeutic target for NSCLC.