BACKGROUND MicroRNA (miRNA) is a small, non-coding RNA molecule which plays a role in the carcinogenesis and progression of cancers. Abnormal expression of miRNA in plasma has been found in some patients with malignant tumors. MATERIAL AND METHODS This study was conducted to investigate the expression of miRNA-30a in plasma of patients with non-small cell lung cancer (NSCLC). The plasma miRNA-30a in 87 patients with NSCLC, 20 patients with benign lung diseases, and 76 healthy subjects were measured by real-time PCR. The diagnostic value of miRNA-30a in NSCLC was evaluated via the ROC curve method. RESULTS Plasma miRNA-30a level was significantly higher in the NSCLC group compared with benign control and healthy control groups (P<0.01). No statistically significant difference was found in the expression level of miRNA-30a among various clinical pathologic features in NSCLC. ROC curve analysis showed that the specificity and sensitivity cut-off points were at 61.0% and 84.3% for NSCLC. The specificity and sensitivity values were 54.9% and 94.4%, respectively, in the analysis based on in-patients only. CONCLUSIONS All these results suggest that plasma miRNA-30a measurement may be a novel and noninvasive method for NSCLC preliminary screening and differential diagnosis.