The purpose of this study was to analyze how a child expresses his psychological status, and how the contents of his expression change in the process of sand-box play and the effect of the application of sand-box play. In accomplishing these purposes, the following research problems were established: 1. How does a child with difficulties in interpersonal cognitive express his psychological status in the sand-box play? 2. What is the effect of the application of sand-box play on a child with difficulties in interpersonal cognitive? The subject of this study was a 6 years and 4 months old male child. The mother of the child visited this researcher to consult about her son who knows the rules and promises in the class and between him and his peers and yet was likely to excessively avoid expressing his emotional expression in front of others. This researcher majored in early childhood education in 4-year college, had 10 years of teaching experiences and is still in service. She completed the basic training for sand-box paly and receives supervision from a developmental expert and a sand- play therapy expert on a regular basis. This study was conducted in the sequence of performing sand-box play, the expression in the sand-box play, and the evaluation. As for the sand-box play tools, sand, a sand-box and play materials were prepared following the methods suggested by Kalff(1966). The sand-box play therapy was conducted over 10 weeks from Jun 16(Wed), 2013 to Aug 28(Wed), 2013 in a total of 10 sessions, 1 session every week. The expression during sand-box play was analyzed by synthesizing the anecdotal records of child s behavioral characteristics, photographs, videotape transcriptions in each session and a child s self-evaluation of the play with focus on the changing process of the sand-box play on the basis of Neumann’s Self-Development Process. Furthermore as for the effect of the application of sand-box play, the changing process of the child between before and after sand-box play was analyzed on the aspect of developmental psychological behavioral characteristics. As for the evaluation tools, Korean-Wechsler Intellignce Scale for Childern-Ⅲ, Bender-Gestalt Test for children, Doll’s House, Kinetic Family Drawing, Self-Esteem Scale for young children, Kindergarten adaptation assessment, House-Tree-Person Test and Peer-Competence Scale were used. The results of the study were as follows: First, when examining the expression in the sand-box play, at the 1st session and the 2nd session, the overall impression was rather poor. As for the spatial arrangement, he divided the whole sand-box for playing. He had difficulties in setting play theme, as for the play material. he used vehicles the most yet his play did not show a consistent pattern, lacking integrity and dynamics, which indicates his ego-development stage was ‘The AnimalsㆍVegetative Phase’. From the 3rd session to the 5th session, his expression showed the pattern of disorder, confusion, confrontation and struggle, ‘Fighting Phase’. In the spatial arrangement, he utilized the whole sand-box space. Moreover, his play developed to more dynamic play over time during sand-box play session. The play themes were battle filed, polar bears and zoo. As for the play materials, he used vehicles and animals the most. The movement of the vehicles had consistent directivity and dynamics and animals were grouped, showing consistent directivity and dynamics as a typical fighting play. In this ego-development, he developed his strength through a trial of strength and Fighting phase. From the 6th session to the 10th session, the spatial arrangement, that converged in the center, drawing a circle in the center of the sand-box, maintained safety during a shift from the balance of power to the integration of power. His expression in the sand-box play showed dynamics and diversity; the theme of disorder disappeared; and the elements symbolizing transformation started