Three fruit by-products namely red peel of pomegranate (exocarp or pericarp), white pulp (mesocarp or albedo) and guava leaves were investigated for their contents of total phenols, total tannins and DPPH radical scavenging activity. The effect of different irradiation doses on these parameters was also studied. The results showed reasonable contents of phenols, tannins and high DPPH radical scavenging activities. Guava leaves indicated the highest radical scavenging activity. The effect of gamma irradiation showed higher antioxidant activity in case of red peel at 30kGy. Lower antioxidant activity was recorded for the white pulp at all doses which was parallel to its tannin contents. Almost no significant change was noticed in the antioxidant activity of guava leaves being extremely high in all cases. Generally, all irradiated fruit by-products studied indicated high antioxidant activities after irradiation. Even in case of the white pulp, which showed the lowest antioxidant activity after irradiation, it retained more than 70% of its natural antioxidant activity. The study recommends using these by-products as food preservatives, supplementary feeds for animals and in preparation of pharmacological products. Guava leaves stabilized by irradiation seem to be the best for food preservation being the highest in antioxidant activity. Keywords : Radiation effects, Antioxidant activity, Fruit by-products.