Patients with cerebral palsy (CP) often experience muscle weakness, resulting in severe impairments that have a negative impact on their ability to perform functional tasks. The current study investigated the association between isometric muscular strength and gross motor performance in children with unilateral cerebral palsy (UCP). Methods: This cross-sectional study was conducted at Private Pediatric Rehabilitation Centers and the Outpatient Clinic at the Faculty of Physical Therapy, Badr University in Cairo, Egypt. The study included 97 children with UCP. The maximum isometric muscle strength of the knee extensors, knee flexors, hip abductors, hip extensors, and paretic lower-limb hip flexors was evaluated by a hand-held dynamometer. The Gross Motor Function Measure (GMFM) of jumping, walking, running, and standing dimensions were determined using the GMFM-66. Results: Knee flexors, knee extensors, hip extensors, hip abductors, and hip flexors showed statistically significant positive correlations with the GMFM-standing and walking dimensions (p < 0.001). Conclusion: Gross motor function significantly correlates with isometric muscle strength in UCP subjects who ambulated with or without an assistive device. This study revealed that strong muscles are required for standing and walking, particularly at the hip and knee joints..