Two experiments were conducted to study effects of feeding different nutritional levels in the earlier growing periods on the performance of Korean native cattle. In experiment I, 14 female calves were divided into two groups and each group assigned to high nutrition or low nutrition feed. Calves of the high nutrition group were fed a calf starter feed of 70.39% TDN and 14.92% DCP during the suckling period of 3 months and a calf grower feed of 71.00% TDN and 12.00% DCP during the growing period until first oestrus. Calves of the low nutrition group were fed a calf starter of 69.90% TDN and 10.60% DCP during the suck]ing period and a calf grower of 63.77% TDN and 9.58% DCP during the growing period. Both groups were suckled and fed roughages in the same way. In experiment II, 28 male calves were divided into two groups and assigned to high and low nutritional levels for the suckling period of 4 months. At the end of the suckling period, each group was again divided into two groups of different nutritional levels for the growing period of 14 months; 7 calves in the high level and 7 calves in the low level. At the end of the growing period, those fed high nutrition dial during the growing period arrived at average body weights over 400 kg and thus were terminated. The remaining animals were continued on a fattening diet which was considered to be of high nutrition for 3 1/2 months. Results obtained from both experiments are summarized as follows; Experiment I 1. Different nutritional levels during the suckling period did not significantly affect the weanling weight of female calves. Significant difference in body weight occurred at the age of 12 months and daily weight gain for the overall period of 24 months was significantly (P $lt;0.05) higher for the high nutrition group than the low nutrition group. 2. Heifers fed the high nutrition consumed more feed in terms of dry matter, DCP and TDN than those of the low nutrition group. However, heifers receiving the high nutrition required less DCP and TDN per kg of body weight gain. 3. Heifers grown on high nutrition diets arrived at the first oestrus significantly (P$lt;0.01) earlier than heifers grown on low nutrition diets. 4. There was no significant difference in amounts of milk secretion between heifers grown on different nutritional levels. 5. Average birth weight of calves from heifers grown on the high nutritional level was significantly (P$lt;0.05) heavier than that of calves from heifers grown on the low nutritional level. Growth rate of the calves was not significantly affected by the nutritional levels fed to their mothers while they were growing. 6. It was concluded that improved reproductive performance of heifers fed high nutritional diet during their early growing period resulted from the early maturity and heavier mature weights of heifers, not from the increased milk secretion nor the rapid growth rate of the offsprings. Experiment II 1. Although nutritional level significantly (P $lt;0.05) affected growth rate of male calves during the suckling and growing periods, nutritional level during the earlier periods did not affect growth rate of calves in the later period Steers fed low nutrition diets during suckling and growing periods gained more weight during the fattening period than those fed a calf starter of high nutrition during the suckling period and fed the same diets afterwards (P$lt;0.05). 2. Calves on high nutritional level consumed more concentrate and less roughages during suckling and growing periods than calves on low nutritional level. 3. There was no significant influence of nutritional level of the feed on the pH of the rumen juice although high nutritional level of growing diet resulted in a little higher production of ruminal volatile fatty acids than low nutritional level. 4. The effect of the nutritional levels of calf starter diet was greater when they were fed a low nutritional growing diet rather than when they were fed a high