Very few studies have investigated predictors of change in various gross motor outcomes in ambulatory children with cerebral palsy (CP). The aim of this study was to identify potential predictors for change in gross motor outcomes measured during various tasks in children with CP. A group of 45 children (age, 6-15 years) with CP and 7 potential predictors were identified, including age, gender, CP subtypes, gross motor function classification system (GMFCS) levels, abdominal muscle endurance, and muscles strength of knee extensor and knee flexor measured by isokinetic dynanometer. Motor outcome was assessed by means of the gross motor composite (GMC) of Bruininks-Oseretsky Test of Motor Proficiency (BOTMP), including four gross motor subtests: running speed and agility (RSA), balance (BAL), bilateral coordination (BCO), and strength (STR). The outcomes were measured at baseline and 12-week later (follow-up). The regression analyses showed that knee extensor strength was a robust predictor of change in BAL, BCO, and GMC (adjusted R[superscript 2] = 0.07-0.19, P less than 0.05). Additionally, abdominal muscle strength was a negative predictor for the changes in the RSA (adjusted R[superscript 2] = 0.08, P less than 0.05). However, STR model revealed no significant predictors. These findings suggest that ambulatory children with greater knee muscle strength may benefit more from therapy than those with lower strength. The knee muscle strength can be used as a biomarker to predict the changes in the gross motor functions. (Contains 4 tables.)