Hyperthyroidism leads to hypermetabolic state with stimulation of high oxygen consumption. This study was undertaken to assess the oxidative stress and antioxidant protective activity in different hyperthyroid states. 50 hyperthyroid subjects and 50 age and sex matched euthyroid controls have been taken. Serum TBARS (thiobarbituric acid reacting substances), as a marker of the free radical mediated oxidative damage was measured. The activity of free radical scavenging enzyme, plasma SOD (Superoxide dismutase) and the serum alpha tocopherol, were measured as markers of the antioxidant status. Hyperthyroid patients had mean T4 value 17.1 ± 1.2 µg/dl (in euthyroid cases 7.99 ± 0.58, p = 0.000), mean TSH 0.14 ± 0.08 µIU/ml (in euthyroid 2.57 ± 0.98, p = 0.000). Mean serum TBARS level in hyperthyroid cases 5.76 ± 0.34 nmol/ml (in euthyroid 2.91 ± 0.22 nmol/ml, p = 0.001), Mean plasma SOD in hyperthyroids 8.24 ± 0.98 IU/ ml (in euthyroid 7.75 ± 0.70, p = 0.01), Mean serum alpha tocopherol 10.28 ± 0.33 mg/L (in euthyroid 12.1 ± 0.27, p = 0.000). Comparison between mean plasma SOD value and mean serum TBARS in hyperthyroid patients show positive correlation and between vitamin E level and TBARS level shows strong negative correlation. Assessment of disturbances in the antioxidant systems might be useful indicator of the susceptibility of patients with hyperthyroidism to free radical damage and suggests usefulness of supplementation with antioxidants in order to prevent oxidative damage in these patients.