Abstract: A definite amount of the dried and powdered sample of Paederia scandens was taken and extracted ultrasonically with mixed solvent of ethanol and water. The active antioxidant components in the extract was reacted with hydroxyl free radical produced by the reaction among Cu2+ ion, ascorbic acid and hydrogen peroxide in the FI-CL analyzer. Based on the change of luminescence intensity ΔI of the CL reaction between H2O2 and luminol, the rate of elimination of hydroxyl free radical by the active antioxidant components of Paederia scandens was determined indirectly. Conditions for extraction of sample and for the CL reaction were studied thoroughly and the optimized conditions were given in detail.