This study examines whether or not sessions of music therapy have positive effect on the childrens learning emotional vocabularies, who have a problem of mild mental retardation, and whether or not the influence from music has any effect on their expression of emotion. The conclusions according to the research results are as follow. First, the results revealed that the program that applied music had a positive effect on improving the learning of vocabularies of emotions, and the effect was sustained in the sustenance evaluation phase after a week of resting phase. This indicates that active use of music to create interests for learning vocabularies played an important role in accelerating linguistic development, and its significance of meaning lies in the fact that music was used not to teach music but as a means to increase linguistic abilities. Second, The results revealed that the four subject children were well developed in their self expressions of their emotions, and displayed a positive effect in the sub-fields such as the field of content expression, voice expression, physical and nonverbal expression and self expression of emotions. Third, it can be said that there the children who participated in the program that utilized music improved on their overall music activities that include music listening, rhythm expressing, singing and instruments handling.