Net energy requirement for maintenance(NEm) in chicks and net availability of metabolizable energy (NE/MEn) of diets were measured by analysis of body composition in 11-26 day old chicks at practical feeding temperature of 14-21℃. Hatched Single Comb White Leghorn male chicks were fed on a commercial chick mash for the first 10 days and for the subsequent 15 days of experimental feeding. And energy retention(ER) was calculated at three times from the body composition in 11-16, 16-21 and 21-26 day old chicks at every 5 days interval and in fasted chicks from I 1, 16 and 21 day old chicks for 3 days each. Daily body weight gain, feed intake, nitrogen balance or retention of protein, lipid and energy were increased in the order of the age of the chicks. The daily energy retention per metabolic body size(㎏^(0.75)) were 73.29, 83.01 and 98.59 ㎉, respectively, in the birds of 11-16, 16-21 and 21-26 day old. When birds were fasted, body weight gain or protein, lipid and energy retention per day were decreased along the lapse of the age. And the dally energy retention per ㎏^(0.75) were -126.56, -145.93 and -124.12 Kcal which were equivalent to heat production at fasting stage(=basal metabolism, BM) of chicks. Metabolizable energy(MEn) of diets were 3.179-3.195 ㎉ per gram and the ratio of MEn to gross energy (GE), MEn/GE, were 76.3-76.7%. In birds of 11-16, 16-21 and 21-26 day old, productive energy(PE) of diet reached to 0.665, 0.748 and 0.850 ㎉ per gram, respectively, which were proportionate to net energy for gain(NEg). And NEg/MEn were shown to be 20.9, 23.4 and 26.6%o, respectively, which were increased significantly (p$lt;0.05) in the order of the passage of the day. Thus NEm/MEn of diet was 37.2%, the ratio of heat increment(HI) to MEn, HI/MEn, was 39.2% and the NE/MEn reached to 60.8%. Daily average NEg, heat production and NEm(=BM) per ㎏^(0.75) were 84.8, 273.1 and 132.9 ㎉, respectively.