The present study was carried out with the aim to evaluate the effect of unilateral and bilateral thyroidectomy on hormonal and biochemical parameters in dogs. Twelve mongrel dogs were rendered to 3 groups with 4 dogs in each group. One group acted as control, in which no surgery was performed, second group underwent unilateral removal of thyroid gland while the third group underwent bilateral removal of thyroid gland. Blood samples were collected preoperatively and at day 7, 15 and 21 postoperatively. TSH, free thyroxine levels, calcium levels and CBC parameters were evaluated. Free T4 level dropped near to zero by day 21 and TSH level rose by many folds in bilateral procedure. On the other hand, in unilateral procedure Free T4 level remained in normal range and 75% of dogs required no levothyroxine therapy. Level of calcium in both procedures remained within normal range. Hemoglobin concentration in both the procedures reduced significantly postoperatively. Result of the study indicate that hypothyroidism is observed in all dogs undergoing bilateral thyroidectomy and there is a need to immediately initiate levothyroxine therapy in these cases. On the other hand, there are 25% chances of postoperative hypothyroidism in dogs undergoing unilateral thyroidectomy. Level of calcium in both procedures remains within normal range provided parathyroid glands are preserved properly. 1482326361.php