The purpose of this study was investigated the onset time of deltoid, trapezius, quadriceps, and tibialis anterior muscle contraction, the order of their contraction, and the gap of onset time between the muscles during sit to standing positions, comparing normal children and children with spastic diplegia. this study group was consists of 10 children with spastic diplegia who were selected at Bundang Bobath Memorial Hospital Rehabilitation Educational Center and Seoul Rehabilitation Hospital. Control group was matched at the same age group with the spastic diplegia children. This study used the superficial electromyography SYNERGY to get the muscle activities of deltoid, trapezius, quadriceps, and tibialis anterior muscle. The onset times of deltoid, trapezius, quadriceps, and tibialis anterior muscle during sit to standing positions were measured and recorded automatically by a computer. The major findings of this study were as follows: (1) Lower part muscles are activated first in the case of normal children, but upper part muscles in the spastic diplegia children. (2) During sit to standing positions, the order of onset time of the muscle contraction was different between normal children and spastic diplegia children. That of spastic diplegia children was trapezius, deltoid, tibialis anterior, quadriceps, but that of normal children was tibialis anterior, trapezius deltoid, quadriceps muscle. Further research is need to investigate the differences in the muscle contraction between normal children and children with spastic diplegia during sit to standing positions.