This feeding experiment was conducted for 6 weeks to study the effect of cobalt supplementation to feed in which the major protein was supplied by either animal or plant sources on growth rate and feed efficiency of young chicks. Day-old 500 female chicks of Fisher line were devided into two groups of animal and plant protein sources, and in each group, five levels of cobalt supplementation (0.0, 0.1, 0.3, 0.6 and 1.0 ㎎/㎏ of feed) were established. The results obtained from this trial were summarized as follows: 1. With the animal protein source, the weight gain obtained with the chicks fed 1.0㎎ of cobalt level was superior to the other, and there was substantial increase in weight gain by feeding cobalt supplemented feeds. 2. With the plant protein source, there were adverse effects on growth rates by feeding cobalt (P$lt;0.05). The growth rates shown with the levels of 0.6 and 0.1㎎ of cobalt were superior to thaw of others. 3. The feed efficiencies achieved by the chicks fed cobalt with animal protein were inferior to those fed cobalt with plant protein, but no statistical difference was found. 4. No toxic effect was observed throughout the experimentation by feeding cobalt supplemented feed.