This research was to assess the effects of art-therapy on a child's improvement of attention/concentration, who is mentally retarded. The purpose of this research was as follows: First, the research purpose to see how significantly art therapy can improve the child's problem. Second, it also wants to see whether art therapy can prolong the child's duration of attention and concentration. Before the start the study, First, we arranged change process by observing and recording each child's behavioral characters on each session. Second, we performed Conners Teacher Rating Scales as a pre-and post-test. Third, we recorded the duration time of attention-concentration on each sessions. Study results obtained through the processes mentioned above are as following: First, to assess the effects of art therapy on improvement in attention/concentration in child with mental retardation, a child's behavior was observed and a comparative analysis was performed by each stage of art activities, showing improvement in attention/concentration and reduction in hyperactivity. Second, results of conducting a comparative analysis of before/after test of Conner's rating scale which was assessed by patients and teachers showed that post-test was higher in score compared with pre-test; we can tell that art therapy influences changes in attention deficit behaviors in child with mental retardation. Third, art therapy improved the duration time of attention/concentration in child with mental retardation. The duration time of attention/concentration in a child involved in this research was prolonged with art therapy program. From the results, we think that children with mental retardation can also improved their attention/concentration by developing contents and teaching methods of art therapy program in consideration of disability characteristics and by applying these to them.