Objectives. The study aimed to test the ethanol extracts of ten medicinal plants for xanthine oxidase inhibitory activity.

Methods. The degree of xanthine oxidase inhibitory activity was determined by measuring the absorbance spectrophotometrically at 290 nm, which is associated with uric acid formation. The selected medicinal plants included Piper lolot C. DC.(Piperaceae), Pandanus amaryllifolius R.(Pandanaceae), Brassica juncea L.(Brassicaceae), Piper betle L.(Piperaceae), Perilla frutescens L.(Lamiaceae), Anacardium occidentale L.(Anacardiaceae), Polygonum barbatum L.(Polygonaceae), Artocarpus Altilis P.(Moraceae), Vitex negundo L.(Verbenaceae), Annona squamosal L.(Annonaceae), which were selected based on folk medicine.

Results. The results showed that the Piper betle L. has a strong ability to inhibit xanthine oxidase with an IC 50 value of up to 1.18 μg/mL, compared to allopurinol 1.57 μg/mL. Different parts of Piper betle L. were compared and the leaves of Piper betle L. showed the best value for xanthine oxidase inhibitory and antioxidant activity.

Conclusions. Piper betle L. showed the best potential for inhibition of xanthine oxidase among ten medicinal plants. Piper betle L. leaf extract showed strong xanthine oxidase inhibitory and antioxidant activity, compared to the whole plant, and the stem extract, which promises to be applied in the treatment of gout.