MicroRNAs (miRNAs) are small non-coding RNAs that function as crucial regulators of gene expression. Recently, dysregulation of miRNA expression in the blood has been demonstrated to be associated with various diseases, including type 2 diabetes mellitus (T2D), suggesting a potential for their use as biomarkers of disease prognosis. The present study examined the expression levels of T2D‑associated miR‑15a in peripheral whole blood samples from patients with T2D, pre‑diabetes individuals exhibiting impaired fasting glucose (IFG) and impaired glucose tolerance (IGT), as well as healthy control subjects, in order to investigate the potential of peripheral blood plasma miR‑15a as a biomarker for the prediction of T2D and pre‑diabetes. The present study included 24 patients with T2D, 22 IFG/IGT individuals and 24 healthy controls. The expression levels of miR‑15a were analyzed by reverse transcription-quantitative polymerase chain reaction. The results indicated that the peripheral blood miR‑15a expression levels were significantly decreased in patients with T2D and IFG/IGT individuals, compared with healthy control subjects (P<0.05). As determined by multivariate logistic regression analysis, lower miR‑15a expression was significantly associated with T2D (odds ratio [OR]; 95% confidence interval [CI]: 0.51; 0.16‑0.73, respectively; P<0.05) and pre‑diabetes (OR; 95% CI: 0.56; 0.23‑0.79, respectively; P<0.05). This association remained statistically significant following adjustment for age, body mass index and hypertension, as well as other biochemical indicators. Furthermore, a receiver operating characteristic analysis revealed that blood miR‑15a distinguished patients with T2D and IFG/IGT individuals from healthy controls (area under the curves; 95% CI: 0.864; 0.751‑0.977 and 95% CI: 0.852; 0.752‑0.953, respectively). These results demonstrated that peripheral blood miR‑15a expression levels were significantly lower in patients with T2D and IFG/IGT individuals, compared with healthy individuals. Thus, miR‑15a in peripheral whole blood may serve as a potential biomarker for T2D and pre-diabetes.