This study was designed to investigate the effects of emulsion formulations of oleuropein isolated from ethanol extract of olive leaf in streptozotocin-diabetic rats. The rats were treated with the administration of the emulsion containing oleuropein at a low (150 mg/kg b.wt.) and high (225 mg/kg b.wt.) dose for 30 days. At the end of the study, blood samples were drawn from the heart of the rats to determine blood glucose, alanine transaminase, and aspartate transaminase levels. In addition, their liver tissues were dissected to determine the levels of glutathione and thiobarbituric acid-reactive substances, and superoxide dismutase activity. According to the results for both dose treatments, a statistically significant increase in superoxide dismutase activities and glutathione levels of the treated diabetic rats was observed when compared with those of the diabetic control rats. On the other hand, a statistically significant decrease in the levels of thiobarbituric acid-reactive substances, aspartate transaminase and alanine transaminase of the treated diabetic rats was determined. It should be highlighted that the administrations at the high dose were more effective compared to that of the low dose. Furthermore, a substantial decrease in the blood glucose levels of the diabetic rats exposed to the high dose was observed.