Effect of environmental temperature (ET) and defeathering (DF) on the thyroid hormone and liver enzyme activity in white Hisex cockerels was examined at 5, 15, 25, and 35℃ of temperature and 0, 50 and 100% defeathering condition. Series of experiment were carried out with three open-circuit respiration chamber. The results obtained are summarized as follows: 1. Serum triiodothyronine (T3) concentrations during fasting were 109, 91, 79 and 69 ng/㎗ respectively under ET of 5, 15, 25, and 35℃, which was revealing the decreasing trend with increasing ET. The level of DF affected on T3 level in the order of 87, 123 and 157.2 ng/㎗ for 0, 50 and 100% DF level respectively. 2. No effect of ET on serem thyroxine (T4) concentration during fasting was observed. The T4 concentration such as 9.1, 9.8 and 10.2 ng/㎗ for increasing degree of DF like 0, 50 and 100% DF treatment. 3. Specific activities of isocitrate dehydrogenase (ICD) were 405, 499, 309 and 241 mu mole/min./㎎ protein with respective ET of 5, 15, 25, and 35℃. 4. Particular trend in the specific activities of citrate cleavage enzyme (ATP-citrate-lyase), due to both ET and the degree of DF, was not observed. However, the activity was generally increased with ;increasing ET.