The aim of this study was to investigate the effects of zinc supplementation on somatostatin and insulin peptide expressions and biochemical parameters. Six- to 6.5-month-old female Swiss albino rats weighing 150–200 g were used. The animals were divided into four groups: group I: control (intact) animals; group II: control animals given zinc sulfate; group III: streptozotocin (STZ)-induced diabetic animals; group IV: STZ-induced diabetic animals given zinc sulfate. Fasting blood glucose and glutathione levels were measured at 0, 1, 30 and 60 days. On day 60, the pancreas tissue and blood samples were taken from the animals. Zinc supplementation caused a decrease in hyperglycemia, as well as weight increase. Zinc sulfate treatment did not affect the number of somatostatin-immunoreactive cells in the pancreas. More insulin-immunoreactive cells were observed in the pancreatic islets of the diabetic + zinc sulfate group than in the diabetic group, although it was not statistically significant. The results show that zinc supplementation may prevent diabetes in experimental animals.