BACKGROUND: Accelerated Pancreatic β-cell apoptosis and oxidative stress are the mainstays of type-1 diabetes. MicroRNA-21's (miRNA-21) role in regulating pancreatic β-cell function remains indefinable. MATERIAL AND METHODS: Five groups of rats were used in this study (healthy controls (Ia), controls that received only chitosan (CS) nanoparticles (NPs)(Ib), streptozotocin (STZ)-induced diabetics rats (II),STZ-induced diabetic rats that received only CS-NPs(III), and STZ-induced diabetic rats treated with mi-RNA-21-CS-NPs(IV). Sera were collected for measurement of fasting blood glucose levels (FBG), insulin, oxidative stress, and intraperitoneal glucose intolerance tests. Pancreatic tissue was collected after sacrifice partly for histological examination and for oxidative stress assessment and evaluation of PTEN/ AKT using qRT-PCR. KEY FINDINGS: We showed over-expression of cleaved-caspase-3 indicating accelerated apoptosis in the β-cell of STZ-induced diabetic rats. Apoptosis was significantly ameliorated by miRNA-21-CS. MiRNA-21-CS-NPs faithfully restored serum fasting insulin, and FBG, and reduced serum and pancreatic oxidative stress markers while enhancing the total antioxidant capacity. Histological examination revealed that miRNA-21 restored healthy β-cell architecture, decreased cleaved-caspase-3, and increased insulin secretion. Transmission electron microscopy revealed increased mitochondrial circularity that significantly correlated with an exaggerated oxidative stress profile as shown by high serum and pancreatic malondialdehyde (MDA), low glutathione peroxidase, and total antioxidant capacity in STZ-induced diabetes. This oxidative profile was reversed using miRNA-21-CS-NPs. Mi-RNA-21 therapy downregulated PTEN but increased AKT and pAKT expression. Altogether, we show that miRNA-21 restored normal islet β-cell structure and insulin secretion through PTEN inhibition. SIGNIFICANCE: miRNA-21- CS-NPs are promising targeted therapeutics that may effectively decrease the global burden of diabetes.