First time application of Acacia nilotica as an ecofriendly antioxidant finishing agent. Reflectance spectroscopic analysis was used to optimize the dye affecting conditions. Dark brown to yellowish shades were obtained with acceptable colorimetric properties. Acacia nilotica finished woolen yarn showed excellent DPPH scavenging activity. Decrease in antioxidant activity as a function of washing cycles followed 1st order kinetic equation.