Methanolic extracts of 27 Thai medicinal plants, traditionally used in different ailments, were evaluated for antioxidant potential using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and oxygen radical absorbance capacity assay (ORAC). In comparison with controls, in the DPPH assay, six extracts (6CD, 22ST, 20SG, 21SpC, 23SV and 14OI) showed higher activities than ascorbic acid (SC50 = 6.07 μg/ml), In the ORAC assay, all species also show good antioxidant capacity (>2 μmole of TE / μg sample). The ORAC values were seem to be correlated with the DPPH values which the six extracts revealed high levels of antioxidant activity according to both methods, and thus could be potential rich sources of natural antioxidants.