MicroRNAs (miRNAs) are a class of small non‑coding single‑stranded RNAs that regulate gene expression at the posttranscriptional level. Since the identification of miRNA, accumulating research has shown their involvement in numerous biological processes, including timing of developmental patterning, embryogenesis, cell differentiation, organogenesis, growth control and pathogenesis of human diseases. It is estimated that >30% human genes may be regulated by miRNA, and that each miRNA can regulate >100 target mRNAs. The widespread and distinct expression pattern of miRNAs in normal and disease states has been extensively investigated in the context of human diseases. Due to the diversity of targets, it is challenging to identify the specific target genes and elucidate the biological function of a certain miRNAs. In the present study, it was confirmed that SMAD7 is a direct target of miR‑21, and overexpression of miR‑21 may inhibit the proliferation of rat renal tubular epithelial cells. These findings confirm the results of previous studies, which have demonstrated that miR‑21 regulates the expression of SMAD7 protein. However, further investigation is required to determine whether miR‑21 is involved in renal development and disease, particularly diabetic nephropathy.