Catechu is considered as one of the most potent herbal medicines use for anti-diarrhea and anti-ulcer. A simple and reliable method to determine (+)-catechin and (-)-epicatechin contents in commercial black and pale catechu was performed by high performance liquid chromatography (HPLC). The antioxidant activities, total phenolic, and total tannin contents of commercial black catechu and pale catechu in Thailand markets were studied. The extracts of some black catechu and all pale catechu showed high antioxidant activities, total phenolic, and non-tannin phenolic contents whereas total tannin contents were quite low. Some black catechu samples were found to be rich source for (+)-catechin and (-)-epicatechin. High (+)-catechin contents were found in all pale catechu whereas (-)-epicatechin were detected at very low concentrations. The main validation parameters of HPLC method were determined. The method was linear over a range of 5-200 μg/ml with high coefficients (r2> 0.99) for both (+)-catechin and (-)- epicatechin. The method also showed good recovery, good repeatability and intermediate precision (%RSD < 3). The results demonstrated that greater amount of phenolic contents lead to more potent antioxidant effect. Moreover, HPLC method can be applied to determine (+)-catechin and (-)-epicatechin contents in plant materials.