10.22376/ijpbs.2019.10.1.p1-12 Volume 4 Issue 1 2013 (January - March) In the present study, free radical scavenging activities of the two plants, lessThan i greaterThan Oroxylum indicum lessThan /i greaterThan (L) Kurz and lessThan i greaterThan Quercus infectoria lessThan /i greaterThan G. Olivier were investigated. Free radical scavenging activities of stem bark of lessThan i greaterThan O. indicum lessThan /i greaterThan and insect galls of lessThan i greaterThan Q. infectoria lessThan /i greaterThan were characterized by the HPLC method developed by D. Chandrashekhar, et al, 2005 using Waters 100 RP-18e column (250 mm × 4 mm, 5 µM) in which stable 1,1-diphenyl-2-picrylhydrazyl (DPPH•) free radical was used. The mobile phase used was a mixture of methanol and water (80: 20, v/v) pumped at a flow rate of 1 ml/min. the DPPH peaks were monitored at 517 nm. In the present investigation it was found that both the plant extracts had remarkable free radical scavenging activities. Ascorbic acid and trolox were used as the standard antioxidants. The IC lessThan sub greaterThan 50 lessThan /sub greaterThan values (inhibition concentration 50) of the ethanolic extracts of stem bark of lessThan i greaterThan O. indicum lessThan /i greaterThan and insect galls of lessThan i greaterThan Q. infectoria lessThan /i greaterThan were found to be 72 ± 2.32 and 58 ± 3.17 µg/ml, respectively as determined by the HPLC method, and correlated well with that determined by colorimetric method, i.e., 71.5 ± 3.64 µg/ml for lessThan i greaterThan O. indicum lessThan /i greaterThan and 61.5 ± 2.42 µg/ml for lessThan i greaterThan Q. infectoria lessThan /i greaterThan . The present study suggested that both the plants have potent antioxidant activity. AMJID AHAD,AJAZ AHMAD GANAI,MOHD MUJEEB AND WASEEM AHMAD SIDDIQUI. antioxidants, dpph, free radical scavenging activity, reversed-phase hplc 397-406