This study was carried out in order to determine the effects of thyroid function upon fattening of the female rabbits. Seventy five female rabbits with an average weight of 2 ㎏ were devided into iodocasein treatment group, tapazol treatment group and control group. Iodocasein treatment group was fed continuously a control ration containing 0.084 g of iodcasein per Kg body weight, and tapazol treatment group 0.25 ㎎ of tapazol. Changes of body weight were observed at an interval of 2 weeks. lifter the pariods of 1, 3, 4, 6 and 8 weeks, the rabbits were sacrificed and then lean meat yield, lean meat percentage and the weight of viscera fat were measured. The results obtained were as follows; 1. Body weight of iodocasein treatment group showed a gradual tendency of decrease by the high significance(P$lt;0.01.) in process of treatment time. Tapazol treatment group showed a trend of a little increase in process of time, reaching to 2262.6±73.39 g, the highest value at the end of experimental periods, but a significant difference was not recognized. 2. Lean meat yield sowed the significance with P$lt;0.05 after 2 weeks and there`s no difference among the neighbouring groups. From 4 weeks after the treatment, in iodocasein treatment group it revealed gradually the decreasing significance with P$lt;0.01 and in the tapazol treatment group the increasing significance (P$lt;0.01), therefore it is recognized that the hypothyroid had an effect on the fattening. 3. Lean meat percentage showed the significance with P$lt;0.05 at each observation time from 4 weeks after the treatment, showing a trend of a decrease in iodocasein treatment group and a increase in tapazol treatment group. 4. Weight of viscera fat showed the marked significance with P$lt;0.01 at each observation time from weeks after the treatment. In iodocasein group it was decreased gradually and 25.0±5.22 g at the end of the experimental period, while tapazol treatment group increased gradually and reached 68.8±6.61 g at the same time.