Aim of the study: The aim of the present study was to investigate an ethanolic extract of Kaempferia parviflora (KPE) reduces oxidative stress and preserves endothelial function in aortae from diabetic rats. Materials and methods: DiabeteswasinducedinSprague–Dawleyratsbystreptozotocin(STZ)treatment (55mg/kgi.v.).Vascularreactivityandsuperoxidegenerationwereassessedinaorticringsusingstandard organ bath techniques and lucigenin-enhanced chemiluminescence, respectively. Results: Eight weeks after STZ treatment blood glucose was elevated compared to citrate treated control rats and there was an increased aortic generation of superoxide anion. In aortic rings acetylcholineinducedrelaxationwasimpairedwhereasendothelium-independentrelaxationtosodiumnitroprusside was unaffected. When aortic rings were acutely exposed to KPE (1, 10 and 100g/ml) there was a significant reduction in the detection of superoxide anion and enhanced relaxation to acetylcholine. Two separate groups of rats (control and diabetic) were orally administered daily with KPE (100mg/kg body weight) for 4 weeks. KPE treatment reduced superoxide generation and increased the nitrite levels in diabetic aortae, and enhanced acetylcholine-induced relaxation. In the presence of NG-nitro-l-arginine (l-NNA),therelaxationtoacetylcholineinaorticringsofdiabeticratswasonlypartiallyinhibited,butwas totallyabolishedinaorticringsfromtheKPE-treateddiabeticrats.Indomethacindidnotaffectrelaxation to acetylcholine in aortic rings of any group. Conclusions:TheseresultssuggestthatKPE,acutelyinvitroorafter4weeksadministrationinvivo,reduces oxidant stress, increases NO bioavailability and preserves endothelium-dependent relaxation in aortae from diabetic rats.