In the present study, the influence of subchronic effects of two plant growth regulators (PGRs) [Abcisic acid (ABA) and Gibberellic acid (GA(3))] on antioxidant defense systems [ reduced glutathione (GSH), glutathione reductase (GR), superoxide dismutase ( SOD), glutathione-S-transferase (GST) and catalase ( CAT)] and lipid peroxidation level ( malondialdehyde MDA) in various tissues of the rat were investigated during treatment as a drinking water model. 75 ppm of ABA and GA3 in drinking water were continuously administered orally to rats (Sprague-Dawley albino) ad libitum for 50 days. The PGRs treatments caused different effects on the antioxidant defense systems and MDA content of dosed rats compared to controls. The lipid peroxidation end product MDA significantly increased in the lungs, heart and kidney of rats treated with GA(3) without significant change in the spleen. ABA caused also a significant increase in MDA content in the spleen, lungs, heart and kidney. The GSH levels were significantly depleted in the spleen, lungs and stomach of rats treated with ABA without any change in the tissues of rats treated with GA(3) except the kidney where it increased. Antioxidant enzyme activities such as SOD significantly increased in the lungs and stomach and decreased in the spleen and heart tissues of rats treated with GA(3). Meanwhile, SOD significantly decreased in the spleen, heart and kidney and increased in the lungs of rats treated with ABA. While CAT activity significantly decreased in the lungs of rats treated with GA(3), a significant increase occurred in the heart of rats treated with both PGRs. On the other hand, the ancillary enzyme GR activity in the tissues were either significantly depleted or not changed with PGRs treatment. The drug metabolizing enzyme GST activity significantly decreased in the lungs of rats treated with ABA but increased in the stomach of rats treated with both PGRs.