Objective: Evaluating the effect of three conventional extraction methods on the extraction yield and antioxidant activity of old tea leaves and black tea wastes extracts, and to compare them with those of green tea leaves. Methods: Tea extracts were obtained by Agarwal, hot water and methanolic methods. Their antioxidant activities were determined according to the thiocyanate method (estimation of two kinetic parameters characterizing the lipid oxidation during its initial stage: stabilization factor F and oxidation rate ratio ORR). Reducing power on iron ion was measured according to the method of Yen and Chen. Results: The highest extraction yield and antioxidant activity were found in hot water extracts of green tea leaves. Hot water extracts of old tea leaves and black tea wastes showed the same statistically significant antioxidant activity (P<0.05). Also, there was not statistically significant difference between the antioxidant activity of old tea leaves and black tea wastes extracts in the other two extraction methods (Agarwal and methanolic methods), and even in some cases, black tea wastes extracts acted better than old tea leaves extracts. The antioxidant activity of tea extracts was not concomitant with the development of their reducing power, which this suggested that the antioxidant activity of tea extracts likely involves other mechanisms in addition to those of reductones. Totally, black tea wastes extracts had the antioxidant activity comparable with or even better than that of old tea leaves extracts. Hence, old tea leaves and black tea wastes, which are often considered as agricultural wastes, can be used as potent natural antioxidative sources. Key words: antioxidant activity, reducing power, extraction, green tea leaves, old tea leaves, black tea wastes.

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