This study investigated the effect of eugenol on arginase, nucleotidase and adenosine deaminase activities in platelets of carrageenan-induced arthritic rat model to explain a possible anti-arthritic mechanism of eugenol. Fifty adult female rats (140-250 g) were divided into ten (10) groups (n = 5). Group I received oral administration of corn oil, group II received 2.50 mg/kg of eugenol, group III and IV rats received oral administration of 5.0 and 10.0 mg/kg of eugenol respectively, group V received 0.20 mg/kg of dexamethasone orally, group VI rats was injected with 1% carrageenan (arthritic rats) and received saline solution orally (arthritic control rat group), group VII, VIII and IX: arthritic rats received 2.50, 5.0 or 10 mg/kg of eugenol orally respectively, group X: arthritic rats was administered with 0.20 mg/kg of dexamethasone orally. The animals were treated for 21 days, thereafter, tibiofemoral histological examination, thiobabituric acid reactive substances level, arginase, nucleoside triphosphate diphosphohydrolase, 5´-nucleotidase and adenosine deaminase activities were assessed. Tibiofemoral histological examination result showed that infiltration of inflammatory cells was significantly decreased with an increase in eugenol dose. Activities of arginase, adenosine triphosphate and adenosine monophosphate hydrolyses were significantly decreased while adenosine diphosphate hydrolysis and adenosine deaminase activities were significantly increased in arthritic rat groups administered with different doses of eugenol. Therefore, eugenol might be a natural complement and alternative promising anti-arthritic agent. These possible anti-arthritic mechanisms may be partly through the modulation of arginase and adenosine nucleotides hydrolyzing enzyme activities as well as the antioxidative action of eugenol.