Non-small cell lung cancer (NSCLC), known as the most common type of lung cancer, has caused great economic losses and brought the patients with NSCLC great suffering. The NSCLC chemo-resistance to cisplatin (DDP) -based chemotherapy remains a huge challenge. The lncRNA growth arrest-specific 5 (GAS5) has been reported to be related with cancers including NSCLC. Phosphatase and tensin homolog (PTEN) has been frequently reported to affect chemo-sensitivity of cancers, and usually acts as a tumor suppressor. In this paper, we demonstrated a significant low GAS5expression in NSCLC patients was correlated with poorer clinicopathologic features; GAS5 knockdown by si-GAS5 transfection promoted NSCLC cell viability. Additionally, GAS5 was involved in the regulation of chemo-sensitivity of the NSCLC cell to DDP through regulation of PTEN pathway. LncRNAs commonly exerts their functions through the interaction with miRNAs. According to previous studies, miR-21 acts as an oncogenic miRNA through targeting PTEN in many cancers. In the present study, GAS5 could compete with PTEN for miR-21 binding. We further verified that the interaction between GAS5 and miR-21 was required in the regulation of NSCLC chemo-sensitivity to DDP through PTEN pathway. Taken together, the data of the present study demonstrated a novel mechanism by which GAS5/miR-21/PTEN affects the sensitivity of NSCLC to DDP-based therapy.