The metabolic syndrome creates risk factors for coronary heart disease, diabetes, fatty liver, obesity and several cancers. Our group has already reported that the essential oil from leaves of Pinus koraiensis SIEB (EOPK) exerted antihyperlipidemic effects by upregulating the low-density lipoprotein receptor and inhibiting acyl-coenzyme A, cholesterol acyltransferases. We evaluated in the current study the anti-diabetic effects of EOPK on mice with streptozotocin (STZ)-induced type I diabetes and on HIT-T15 pancreatic β cells. EOPK significantly protected HIT-T15 cells from STZ-induced cytotoxicity and reduced the blood glucose level in STZ-induced diabetic mice when compared with the untreated control. EOPK consistently and significantly suppressed the α-amylase activity in a dose-dependent manner and enhanced the expression of insulin at the mRNA level in STZ-treated HIT-T15 cells, while the expression of insulin was attenuated. EOPK also significantly abrogated the population of reactive oxygen species when compared to the untreated control in STZ-treated HIT-T15 cells. Furthermore, EOPK significantly reduce nitric oxide production, suppressed the phosphorylation of endothelial nitric oxide (NO) synthase and suppressed the production of vascular endothelial growth factor (VEGF) in STZ-treated HIT-T15 cells, implying its potential application to diabetic retinopathy. Overall, our findings suggest that EOPK had hypoglycemic potential by inhibiting reactive oxygene species (ROS), endothelial NO synthase (eNOS) and VEGF in STZ-treated mice and HIT-T15 pancreatic β cells as a potent anti-diabetic agent.