This paper aims to design a system for psychological diagnosis in sandbox play by applying rule based
expert system. Sandbox play is one of play therapy and it is a technique that can be combined with
psychological diagnosis and treatment using sand and various kinds of figures. In this technique, we focus
on psychological diagnostic factors and try to implement a system that automatically diagnoses
psychological types when input values are given. Therefore, six kinds of language objects are set and the
rules are created according to the types of figures, arrangement of figures, and production time in the sand
box used as a reference element in the diagnosis method. In this system, it is assumed that the client
recognizes the finished sandbox as a sensor device. Then, when the recognized state enters the input value,
the rules based on the language object are ignited in order. Through this, the client is diagnosed with one
of 26 types of psychology. As a result, the diagnostic process is simplified and automated. Accordingly, a more detailed psychological diagnosis and treatments are provided.