GLC analysis of organic acids of different fruit components (flavedo, albedo, and juice) was carried out by a modified method. ‘Shamouti’ orange fruits (Citrus sinensis (L.) Osbeck) were of different viability because of progressive aging during postharvest storage (3 months at 17°C). Wide quantitative and qualitative differences in acid composition of tissues were detected. Citric was the main acid in juice, malonic and malic in peel tissues. Additional acids included succinic, adipic, isocitric, oxalic, lactic, aconitic, α-ketoglutaric and benzoic. With tissue aging, malonic, succinic and adipic acids concentration increased in peel and juice, but citric and malic acids concn decreased in juice. Malonic acid, the competitive inhibitor of acid respiration, can serve as an indicator of fruit tissue senescence, because its accumulation in the peel begins at fruit maturity, and increases threefold during 3 months post harvest. Moreover, it is the acid component most closely linked with aging of fruit tissues as determined by softness and deformation parameters.