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This paper reports a comparative study of the antioxidative effects of black and green tea extracts in sodium oxalate-challenged rats. A dose of 10 mg/kg of body weight of sodium oxalate was used to induce lipid peroxidation in vivo. Rats treated with sodium oxalate had 42.06 ± 3.10 nM/hour, 45.39 ± 9.75 mg/100 mL, 10.95 ± 1.52%, 15.95 ± 3.19 mg/dL, 112.25 ± 5.15 mg/dL, 59.21 ± 2.95 IU, 39.55 ± 2.51 IU, and 150.62 ± 9.62 KA/unit for serum levels of malondialdehyde, reduced ascorbic acid, catalase, cholesterol, phospholipid, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP), respectively. These values are significantly (P < .05) different from values obtained from normal rats. Rats pretreated with 100 mg/kg of body weight of green tea had 27.59 ± 3.56 nM/hour, 79.11 ± 5.13 mg/100 mL, 4.23 ± 0.36%, 50.09 ± 5.24 mg/dL, 97.58 ± 4.73 mg/dL, 23.10 ± 1.59 IU, 31.14 ± 1.26 IU, and 96.48 ± 2.36 KA/unit for serum levels of malondialdehyde, reduced ascorbic acid, catalase, cholesterol, phospholipid, AST, ALT, and ALP, respectively, compared with 37.28 ± 2.07 nM/hour, 72.62 ± 2.10 mg/100 mL, 6.23 ± 1.52%, 37.25 ± 2.84 mg/dL, 78.05 ± 2.36 mg/dL, 36.08 ± 1.80 IU, 29.00 ± 3.02 IU, and 109.23 ± 6.32 KA/unit recorded for the same parameters in rats treated with black tea. The cholesterol to phospholipid ratio was increased from 0.14 ± 0.04 in control rats to 0.47 ± 0.02 and 0.51 ± 0.01 by black and green tea extracts, respectively. These results suggest that tea extracts have antioxidant properties and that green tea extract is more potent.