The aim of this study was to determine the effects of balanced deep-sea water (BDSW) on hyperglycemia and glucose intolerance in streptozotocin (STZ)-induced diabetic mice. BDSW was prepared by mixing DSW mineral extracts and desalinated water to yield a final hardness of 1000–4000 ppm. Male ICR mice were assigned to 6 groups; mice in each group were given tap water (normal and STZ diabetic groups) or STZ with BDSW of varying hardness (0, 1000, 2000, and 4000 ppm) for 4 weeks. The STZ with BDSW group exhibited lowered fasting plasma glucose levels than the STZ-induced diabetic group. Oral glucose tolerance tests showed that BDSW improves impaired glucose tolerance in STZ-induced diabetic mice. Histopathological evaluation of the pancreas showed that BDSW restores the morphology of the pancreatic islets of Langerhans and increases the secretion of insulin in STZ-induced diabetic mice. Quantitative real-time PCR assay revealed that the expression of hepatic genes involved in gluconeogenesis, glucose oxidation, and glycogenolysis was suppressed, while the expression of the genes involved in glucose uptake, β-oxidation, and glucose oxidation in muscle were increased in the STZ with BDSW group. BDSW stimulated PI3-K, AMPK, and mTOR pathway-mediated glucose uptake in C2C12 myotubes. BDSW increased AMPK phosphorylation in C2C12 myotubes and improved impaired AMPK phosphorylation in the muscles of STZ-induced diabetic mice. Taken together, these results suggest that BDSW is a potential anti-diabetic agent, owing to its ability to suppress hyperglycemia and improve glucose intolerance by modulating glucose metabolism, recovering pancreatic islets of Langerhans and increasing glucose uptake.