This study aims at the close examination of the advanced performance through the key-music al-instrument mediation program, clarification of the degree of mediation time through the color note for the students with mental retardation, and the research of whether or not to maintain the acquired performance ability after the mediation program. To conduct this research, three students in J school were chosen who distinguish color, read and write the musical scale of Do Re Mi Fa Sol La Si and Do in Korean letter, and can play tunes in accordance with his or her teacher\'s directions. Total 24 surveys were conducted every week (sixty minutes per a survey), of which the term was 7 months. Numerousness was basis of the research plan. The proportion of the correctness of which the criterion was the correct response to the scales of the tune was reckoned by dividing the numbers of the scales by the correct numbers of the scales of the tune and multiplying a hundredfold. The conclusions of this study are as followings. First, the mediation through color note has a great effect on the improvement of the performa nce of the key-musical-instrument of the students with mental retardation. Second, to show their own perfect performance requires 6~10 mediations. Third, it is made clear that their advanced performing ability lasts after the close of the mediation.