is a member of the miRNA family and one of the top expressed miRNAs in human islets that implicated in glucose homeostasis. The levels of in type 2 diabetes (T2DM) patients or its role in β-cell function is still unclear. In the current study, we measured the serum levels of in Emirati patients with T2DM (with/without complications) and control subjects. Overexpression or silencing of in INS-1 (832/13) cells was performed to investigate the impact on insulin secretion, content, cell viability, apoptosis, and key functional genes. We found that serum levels of are significantly (<0.05) higher in T2DM-patients or T2DM with complications compared to control subjects. Overexpression of increased insulin content and decreased glucose-stimulated insulin secretion, whereas silencing of reduced insulin content and secretion. Modulation of the expression levels of did not influence cell viability nor apoptosis. Analysis of mRNA and protein expression of hallmark genes in transfected cells revealed a marked dysregulation of , Pancreatic And Duodenal Homeobox 1 (), and . In conclusion, an appropriate level of let7b-5p is essential to maintain β-cell function and may be regarded as a biomarker for T2DM.Let7b-5p