The purposes of this study were to examine inter-rater reliability of the Manual Ability Classification System (MACS) by children's age and to identify the correlation between the MACS and the Gross Motor Function Classification System (GMFCS) in children with cerebral palsy (CP). Twenty-six children with CP older than two years participated. Children with CP were classified according to the MACS and the GMFCS by two physical therapists. Inter-rater reliability was analyzed using the Intraclass Correlation Coefficients (ICCs). The results showed that the reliability of the MACS for children aged 2~3 years was .88 and for children aged above 4 years was .98 (p<.05). Children with quadriplegia had a higher level of MACS than children with spastic hemiplegia and diplegia. A moderate relationship between the MACS and the GMFCS was found in all children (rater 1, r=.631; rater 2, r=.438). The MACS will be used for classification of children with CP according to the manual abilities. Thus, it offers a reliable method for communicating between therapists about the manual ability of children with CP who are older than 2 years.