Diabetes mellitus (DM) is a disease related to metabolic disorder and becoming an epidemic in developing countries. Current treatments for DM include modified lifestyle practice, obesity treatment, oral hypoglycemic agents, and insulin sensitizers, yet no cure is available in sight for the disease, despite it requires new insight into the molecular and pathophysiology. MicroRNAs (miRNAs) are small noncoding RNAs considered as of greater biological importance and controls molecular signaling pathways in diabetic pathogenesis. The microRNA 21 is an important microRNA frequently upregulated in all types of diseases suggesting that it plays an important role in cell proliferation, and apoptosis. The present mini review highlights the recent investigations related to the importance of miR-21 in different types of DM based on the up-to-date reports.