Background. Strength training programs for children with cerebral palsy (CP) showed inconclusive evidence for improving walking, despite improvements in strength. Recent studies have suggested that strength training with high movement velocity is more effective for improving walking than traditional resistance training. Objective. The purpose of this study was to evaluate the effect of functional high-velocity resistance training (power-training) to improve muscle strength and walking capacity of children with CP. Method. Twenty-two children with spastic CP participated (13 bilateral, Gross Motor Function Classification System [GMFCS] level I [n = 10] and II [n = 12], 7.5 years [SD 1.8, range 4-10 years]). Within-subjects changes in a 14-weeks usual care period were compared with changes in a 14-week functional power-training period (in groups, 3×/wk). Outcome measures were the muscle power sprint test (MPST), 1-minute walk test (1MWT), 10-m shuttle run test (SRT), gross motor function (GMFM-66), isometric strength of lower-limb muscles and dynamic ankle plantar flexor strength. Results. Changes during the training period were significantly larger than changes in the usual care period for all outcome measures (P <.05). Large improvements were found during the training period for walking capacity (δMPST [mean]: 27.6 W [95%CI 15.84-39.46, 83% increase], δ1MWT: 9.4 m [95% CI 4.17-14.68, 13%], δSRT: 4.2 [95%CI 2.57-5.83, 56%], δGMFM-66: 5.5 [95% CI 3.33-7.74, 7%]) and muscle strength (18%-128%), while outcomes remained stable in the usual care period. Conclusions. The results indicate that functional power-training is an effective training for improving walking capacity in young children with cerebral palsy.