Tetrahydroamentoflavone, a potent XO inhibitor isolated and purified from the herbs of Selaginella uncinata, exerts its antioxidant activity in vitro through metal-chelating, and radical-scavenging, and has anti-inflammatory effects. It shows in vitro cyclooxygenase (COX) inhibition activity ( an IC(50) value of 29.5 microM (COX-1) and 40.5% inhibition at 100 mg/mL (COX-2)).