Understanding the molecular mechanism by which epithelial mesenchymal transition (EMT)-mediated cancer metastasis and how microRNA (miRNA) regulates lung cancer progression via Twist1-activated EMT may provide potential therapeutic targets for cancer therapy. Here we found that miR-33a, an intronic miRNA located within the sterol regulatory element-binding protein 2 (SREBP-2) gene, is expressed at low levels in metastatic non-small cell lung cancer (NSCLC) cells and is inversely correlated with Twist1 expression. Conversely, miR-33a knockdown induces EMT and miR-33a overexpression blocks EMT by regulating of Twist1 expression in NSCLC cells. Bioinformatical prediction and luciferase reporter assay confirm that Twist1 is a direct target of miR-33a. Additionally, Twist1 knockdown blocks EMT-related metastasis and forced expression of miR-33a inhibits lung cancer metastasis in a xenograft animal model. Clinically, miR-33a is found to be at low levels in NSCLC patients and down-regulation of miR-33a predicts a poor prognosis. These findings suggest that miR-33a targets Twist1 and inhibits invasion and metastasis in NSCLC. Thus, miR-33a might be a potential prognostic marker and of therapeutic relevance for NSCLC metastasis intervention.