This study has been conducted in an attempt to measure the effect of dance and movement therapy on the emotional expression and sociality of people with mental retardation and for the purpose, dance/movement therapy programs had been run for 14 weeks, once a week, from Jan. 3 to Apr. 4, 2003 at day caring centers for mentally retarded persons in Seoul. This study has been conducted for 10 male and female mentally retarded persons at day caring centers, including 3 persons with grade 1 mental retardation, 4 persons with grade 2 and 3 persons with grade 3 of the ages between 22 and 42. For the six persons with grade 2 and 3 mental retardation (IQ 45-70), scores that they had got at the sociality and emotional expression property test developed by Miller and Sullivan in 1982 conducted before and after the implementation of dance/movement therapy program were compared in addition to the observance and record of the progress of dance/movement therapy. For 3 persons with grade 1 mental retardation(IQ 34) and a person with grade 2 mental retardation along with autism, developments by the progress of dance/movement therapy were observed and recorded. Dance/movement therapy program consisting of total 14 sessions organized in accordance with assignments by steps had been conducted divided in the steps for social development and the steps for emotional expression development, and a session program lasting 50 minutes was divided into five steps of Warm-up - Release - Development of theme - Centering - Closure. In the comparison of questionnaire scores before and after the implementation of dance/movement program that was conducted divided into emotional expression and sociality, 2 persons among the six subject persons showed the same scores before and after the program implementation, while the remaining four persons recorded increased scores from 1 to 3 in emotional expression. In the sociality test, 2 persons among the six subject persons showed the same scores before and after the program implementation, while the remaining four persons recorded increased scores from 1 to 4, which proves that their emotional expression and sociality had been improved by the implementation of the program. Observance of developments according to the progress of the program showed that with the beginning of the dance/movement program for sociality development, participators positively expressed their desire to participate and formed relations with others as their awareness of their bodies grew, thus making the whole group dynamic. In the step for emotional expression development, participators were familiar with expressing their emotion and positive attitude within the program thanks to the movements and mutual relations they had acquired at the step for sociality development. Experience of the participators with the trust in the group, interaction and leadership at the step for the sociality development enabled the participators to recognize themselves and caused changes to their caring and concerns for others, and based on the development, they could be aware of their own emotions and positive attitude, and emotionally express their future possibility. In conclusion, this study proved that dance/movement therapy that uses physical movements as psychological therapy tools was effective in improving emotional expression and sociality of the mentally retarded persons, and in the context, clinical application of dance/movement therapy is expected to help mentally retarded persons with emotional expression and sociality.