As a part of my investigations about natural antioxidants from local medicinal plants of Bangladesh, i would like to analyze the phenolic compounds present in plant extract by using HPLC-diode-array detection system and evaluate the antioxidant activities in vitro by using DPPH radical scavenging assay, reducing power assay, super oxide radical scavenging assay, hydrogen peroxide radical scavenging assay, total antioxidant capacity assay etc.