The effects of Aegle marmelos (Rutaceae) leaf, Emblica officinalis (Euphorbiaceae) fruit and Ocimum sanctum. (Labiateae) leaf extracts were studied in L-thyroxine (0.5 mg/kg) induced hyperthyroidic mice. Separately combined effects of these three plant extracts and of a commonly used antithyroidic drug, Propyl thiouracil (PTU) were investigated for comparison. Serum concentration of thyroxine $(T_4)$, triiodothyronine $(T_3)$, glucose and the activity of hepatic Glucose 6-Phosphatase (G-6-Pase) were considered as main parameters. Hepatic lipid peroxidation (LPO), superoxide dismutase (SOD) and Catalase (CAT) activities were also studied to reveal the toxic effect of the plant extracts, if any. While exogenous $T_4$ enhanced serum concentration of $T_4$, $T_3$, glucose and the activity of hepatic G-6-Pase, a simultaneous administration of either A. marmelos leaf (1.0 mg/kg), E. officinalis fruit( 30 mg/kg) and O. sanctum leaf (50 mg/kg) extracts, to hyperthyroidic animals decreased all these parameters. However, the effects were more pronounced, as nearly normal thyroid function and serum glucose concentration were exhibited when all three plant extracts were administered together. A decrease in LPO and a concomitant increase in SOD and the CAT activities indicated the safe and antiperoxidative nature of the plant extracts, administered either alone or in combination. Our findings reveal that the three test plant materials exhibit synergistic effects without any hepatotoxicity, suggesting their potential use in the amelioration of hyperthyroidism and/ or hyperglycaemia.