Cannabidiol (CBD) decreases insulitis, inflammation, neuropathic pain and myocardial dysfunction in preclinical models of diabetes. We recently showed that CBD also improves vasorelaxation in the Zucker Diabetic fatty (ZDF) rat, and the objective of the present study was to establish the mechanisms underlying this effect. Femoral arteries from ZDF rats and ZDF lean controls were isolated and mounted on a myograph and incubated with CBD (10 µM) or vehicle for 2h. Subsequent vasorelaxant responses were measured in combination with various interventions. Prostaglandin metabolites were detected using enzyme immunoassay. Direct effects of CBD on cyclooxygenase (COX) enzyme activity were measured by oxygraph assay. CBD enhanced the maximum vasorelaxation to acetylcholine (ACh) in femoral arteries from ZDF lean (P<0.05) and especially ZDF rats (P<0.0001). In ZDF arteries, this enhancement was not affected by CB1, CBe or PPARγ antagonism, but was inhibited by CB2 receptor antagonism. CBD also uncovered a vasorelaxant response to a CB2 agonist not previously observed. The CBD-enhanced ACh response was endothelium-, nitric oxide- and hydrogen peroxide-independent. It was, however, COX1/2- and superoxide dismutase-dependent. CBD enhances the activity of both purified COX-1 and COX-2. The CBD-enhanced ACh response in the arteries was inhibited by a prostanoid EP4 receptor antagonist. PGE2 metabolite levels were below the limits of detection, but 6-keto PGF1α was decreased after CBD incubation. CBD exposure enhances the ability of arteries to relax via enhanced production of vasodilator COX 1/2-derived products acting at EP4 receptors.