This study analyzed lower extremity muscle activity and pelvic tilt in children with spastic diplegia in standing. The subjects of this study were 8 normal children and 8 children with spastic diplegia who have been treated in Bobath hospital. The groups of children were evaluated with inclinometer and EMG. The EMG activities of the gluteus maximus, rectus abdominis, medial hamstring and rectus femoris were recorded by surface electrodes while standing. The findings of this study were as follows. First, significant differences of pelvic tilting were found between children with spastic diplegia and normal children(p<0.05). Second, the root mean square(RMS) of gluteus maximus and rectus abdominis in standing was not significantly different between them. But there were difference of RMS of medial hamstring and rectus femoris in standing(p<0.05). Third we found a linear relationship between pelvic tilt and RMS of each muscle. There was a negative relationship between pelvic tilt and RMS of rectus femoris in children with spastic diplegia(r2=0.596, p=0.025) and a positive relationship between pelvic tilt and RMS of gluteus maximus(GM) and rectus femoris(RF) in normal children(GM: 12=0.535, p=0.039, RF: 7*=0.703, p=0.009). The result suggest that the rectus femoris be strengthened and medial hamstring be released to decrease the anterior tilt of the pelvis as an effective solution to the problem with standing in children with spastic diplegia. Further studies are needed to determine what effect orthopedic operations might have on pelvic tilt during standing.