As a part of synthetic analysis of infant-physical fitness, (from 4 to 7 years old) the relationship of the physical characteristics and birth order to reaction time was exmained. Following results were obtained : 1) The development of older children's physique was better than that of younger children (p<00.5-0.005). 2) In releation to the birth order and physique, boys of first birth were better than third birth (p<0.05-0.005); but girls of third birth were better than first birth (p<0.05-0.005). 3) In relation to the physique and speed of reaction time, side step test, standing reacton ti...