The methanolic extract of Spatoglossum asperum showed radical scavenging activity against DPPH, ABTS, superoxide and nitric oxide radicals. Although the concentrations of methanolic extract of S.asperum. for antioxidant activity were much higher than that of standard drugs when tested in various assays, their maximal effects were approximately the same. For antioxidant activities, the methanolic extracts showed an increase with increasing concentration (between 100 and 900 μg/ml) indicating the dose dependency of these algal extract. The significant free radical scavenging activity of Spatoglossum asperum indicated that it could be a potential source of natural antioxidant lead molecules.