Abstract: The purpose of this study was to evaluate the effect of calf muscle strengthening on standing function and posture in spastic diplegic cerebral palsied children. Thirty spastic diplegic children with age ranged from 2-4 years participated in this study. They were assigned randomly into two groups of equal numbers, control (A) and study (B). Each patient of the two groups was evaluated before and after treatment by using standing dimension of Gross Motor Function Measure-88, AutoCad 2007 software program for measuring knee and ankle joints angles in sagittal plan during standing and ultrasonography for measuring calf muscle thickness before and after three successive months of application of the treatment programs. The control group received a selected physical therapy program for one hour per session. The study group received the same selected physical therapy program given to the control group for one hour in addition to strengthening exercises and electrical stimulation program for calf muscles of both lower limbs. The program of treatment was conducted at 3 times/week basis for three successive months. The pre-treatment results revealed no significant difference in all measured variables between the two groups. While significant difference in all measured variables between the two groups were recorded after the treatment period in favor of the study group. These results show the importance of strengthening the calf muscles in spastic diplegic children.