To investigate the relations between the balance function and gross motor ability, we recruited 15 children with cerebral palsy from 5 to 12 years in age. Balance function was tested by the Smart Balance Master System and by clinical tests. The Motor Age test was used to test gross motor ability. Analysis showed that postural stability in eyes open, eyes closed, and swaying vision conditions (visual surrounding swaying with body sway), the duration of one leg standing, and the duration of maintaining a heel-to-toe position were significantly correlated with gross motor ability. Postural stability in the eyes-closed condition was the best predicting factor and could explain 64% of the variability of gross motor ability. Whether the training of postural stability in eyes-closed condition can improve the gross motor function needs further study.