The object of the present study is to examine the effect of physical training during early growth of life on body weight gain and physical performance. Early weaned (2 weeks after birth) male mice were divided into control and training group-and experimental period was divided into growing period (from 1st week to 6th weeks after weaning) and adult period (from 7th weeks to 9th weeks after weaning). Physical training was. given on a small animal treadmill with a speed of 34.3m/min and 19℃ slope and both groups of body weight gain and maximal running time on the treadmill were determined. The results obtained are summarized as follows; 1. Body weight gain was lesser in training group than control group and the difference was. statistically significant at 1, 2.5, 5.7 weeks of training period. 2. Maximal running time of training group was found to be longer than that of control group at 6th (p<0.01), 8th (p<0.001) and 9th weeks. (p<0.01). From the above results, it may be concluded that if physical training is started in early growth of life, there might be an improvement of physical performance.