The main purpose of this research was to explore how a child with selective mutism used sand, water, miniatures and other media to express his internal experiences and how his communicative behavior changed in his daily life. Case study was adopted as the methodology for this research. The object studied was an elementary school third grader who had selective mutism. He was a referral by a doctor in a child development center. Before giving the sandplay therapy, the object and his mother were consulted. Then, a twenty-session therapy was followed. Each session lasted for 40 minutes. During the research period, interviews with the parents and his teacher were often conducted. The conclusions of this study are as the following: 1.During the therapy process, development stages of behavior were observed in his sand-play, which include the exploration over the sand-tray, the self-expression, self-nutrition, and the psyche situation that moved from consciousness to sub-consciousness. After working off his internal conflicts, the case gained the confidence to face his problem and think about the resolutions. 2.The case takes a few miniatures signaled the problem of adaptation. Another sign that he never chose human miniatures signaled the mutism had generated problems in his interaction with others. The case takes miniatures and puts back are usually of particular meanings as they imply the case's negative emotion or internal conflicts. 3.During the therapy, positive changes from the case's behavior were noticed in mother-son relationship, the peer relationship and the conceptions toward the outer world. 4.After the sandplay therapy, the case gained noticeable improvement in communicating with others. Accordingly, recommendations and suggestions were made for the future therapies' and researchers' reference.