The purpose of this study is to find out a weight control criteria corresponding to physical fitness factors and levels achievement. The subjects are twenty two Boxers of Seoul Athletics high school. The methods are compared the physical fitness after measurement the physical fitness of normal weight and that of weight reducing at the rate of 1/25, 1/20, 1/15, 1/12 respectively. The results of this study have been concluded as follows; 1) Physical fitness declines in proportion to the quantity of weight reduction in the whole physical fitness factors. 2) A remarkable physical fitness change doesn’t occur when one-twenty-fifth normal weight is reduced. 3) A phenomenal physical fitness change took place in the upper-arm’s muscle endurance in case one-twentieth reduction of normal weight is made. If, therefore, one has a hard-training to develop one’s upper-arm’s muscle endurance, one’s physical fitness can’t be effected even when one-twentieth of normal weight reduced. 4) One-fifteenth reduction of normal weight brings about the decline in the physical fitness exept the flexibility and agility. According above one-fifteenth reduction of normal weight is not encouraged as it causes the decline in the physical fitness. 5) One-twelfth reduction of normal weight brings about the drop in the whole physical fitness factors exept flexibility. 6) According as weight drops, factors that remarkably cause the decline in the physical fitness is that upper-arm’s muscle endurance, comes next to balance, and to abnormal muscle endurance, This is to mean that comparatively muscle endurance brings about the most phenomenal decline in the physical fitness. 7) Flexibility can’t come under the influence of weight change.