In clinically, rehabilitation therapy is focused on functional improvement in mild to moderate cerebral palsy (CP) patients. In severe cases, postural management is one of the target goals. Therapeutic intensity is various in each patients and optimal intensity is still unclear. The aim of this study is to assess relation between therapeutic intensity of rehabilitation therapy and functional improvement in CP patients. Participants were 39 children with spastic CP. We divided participants into two groups based on initial gross motor function classification system (GMFCS) level, as mild to moderate groups with GMFCS 1 to 3, and severe groups with GMFCS 4 and 5. We also divided subjects into three groups based on intensity of therapy. We defined low intensity as less than 7 sessions (30 minutes of therapy per session) per week, intermediate intensity as 7 to 14 sessions per week and high intensity as over 14 sessions per week. Gross motor function measure (GMFM) and pediatric evaluation of disability inventory (PEDI) (three domains of Self-care, Mobility and Social) were measured at initial and 6 months by qualified investigators. Statistically significant improvement was observed in GMFM scores and mobility scores of PEDI in mild to moderate group ( P < 0.05), self-care and social function sub-scores of PEDI in severe group ( P < 0.05) for 6 months. Rehabilitation therapy with high intensity showed gross motor function improvement in mild to moderate group. In severe group, high intensity therapy showed improvement of self-care and social function than gross motor function in same duration. To our knowledge, high intensity rehabilitation could make more functional and postural improvement in CP patients. However, there are many variables such as age, GMFCS level, type of CP, medical condition, comorbidities, etc. Consideration about optimal intensity of rehabilitation therapy according to severity of disease is needed in further study.