T he purpos e of this study was to ex amine the effect s of the mu sic act ivit ies in th e tr eatment of maladapt iv e beh avior of ment ally r et arded childr en . Sev en childr en h avin g seriou s maladaptiv e beh avior in the ag e of 9 to 9 par t icipat ed in this r es ear ch . T h e K- ABS Adapt iv e Behav ior T est , st andardized by Seun g - Kook Kim (1990), was u sed to measur e fiv e s elected ar eas of maladaptiv e beh avior : (1) violent an d dest ructiv e behavior , (2) r ebelliou s b ehavior , (3) with dr awal, (4) hyperactiv e behavior , an d (5) ant isocial behav ior . In addition , att ention behavior wa s also measur ed by u sin g t ime sampling method. Mu sic act ivit ies u sed in this r esear ch con sist ed of nine in st rumental an d non - in st rument al activities . Dur ing th e six week s , this resear ch er and the other co- ther apist worked t og ether for 3 pr e- t est in g ses sion s , 18 mu sic ses sion s , and 4 post - t est in g ses sion s . T he r esult s showed that maladapt iv e behav ior significantly decr eased par t icularly in the ar eas of violent an d dest ruct iv e b ehavior , r ebelliou s behavior , with dr awal, and hyper act iv e behav ior aft er the part icipation (p< .05). Ant isocial behav ior was also dropped n ot iceably but not en ou gh y et t o meet st at ist ical significan ce (p=.051). Att ention beh avior was also significantly in cr eased (p< .01). In st rumental act ivit ies wer e foun d t o be v ery adv ant ag eou s for th e childr en \' s att ention span .