Abstract: Background and Objectives: Different studies indicated association of isoniazid (INH) treatment with different adverse reactions. Green tea catechins (GTC) showed antioxidative activities in different reports. The aim of this study was to assess the antioxidative activity of GTC against the INH-induced alterations in certain serum lipids and liver function biomarkers in addition to certain endogenous antioxidants. Materials and Methods: One hundred male albino rats were randomly divided into four groups: control, INH-treated, (INH+GTC)-treated and GTC-treated groups. The INH and GTC were orally administered at dose levels of 27 and 50 mg kg–1 b.wt., respectively, daily for 5 weeks. Statistical analysis was performed using t-test and one-way analysis of variance (ANOVA). Results: In the INH-treated animals, the lipid profile showed high levels of most serum lipids. Liver function biomarkers were elevated indicating hepatic affection. Oxidative stress was reflected in the increased liver malondialdehyde (MDA) content and decreased hepatic glutathione (GSH) level and superoxide dismutase (SOD) and catalase (CAT) activities, in addition to the reduced activity of erythrocyte G6PD. Yet, the administration of GTC 1 h prior to the INH resulted in the alleviation of these alterations. Conclusion: The co-administration of GTC with the INH ameliorated the INH-induced alterations in serum lipids, liver function biomarkers and antioxidant systems.