Upper motor neuron lesions are characterized by spasticity, which impairs motor abilities necessary for daily activities and can also result in structural alterations in the muscle which can be detected by ultrasonography. The study's aim was to dictate the effects of spasticity in children with cerebral palsy (CP) on functional abilities and the length of the quadriceps fascicle (QFL). Methods: The study's inclusion was constrained to 100 CP children, 50 of them were spastic and the other 50 were normal. Their ages were from four and six years, and they were able to stand with holding on. The functional abilities were evaluated using the Gross Motor Function Measure-88 (GMFM-88), The degree of spasticity was evaluated using the Modified Ashworth Scale (MAS) and QFL was assessed by Ultrasonography (US). Results: There was a substantial variation in (QFL) comparing the spastic and normal groups (p> 0.05), as well as a significant association between spasticity and (QFL) (p> 0.05) and between spasticity and functional skills (p> 0.05). Conclusion: In children with spastic CP, spasticity has a considerable impact on (QFL) and functional abilities