The purpose of this case study was to examine the improvement in sociality of preschoolers through group art therapy using ETC (the expressive therapies continuum). Regarding the subjects of this study, the preliminary observation was conducted of six-year old children whose sociality needed to be improved in a daycare center of S city. Four who received scores lower than the average (109) of total score (200) on the Korean Social Skill Rating Scale for Preschoolers (K-SSRSP) were finally selected. A total of 13 sessions of therapy were provided for 60 minutes per session once a week from September 2019 to December 2019. As the research tool, this study quantitatively and qualitatively analyzed the K-SSRSP and then researchers conducted the qualitative analysis of each session according to the developmental hierarchy of ETC. The results of this study were as follows: First, the score of K-SSRSP was improved, which had positive effects on the sociality. Second, each level of ETC led to the strengthening of solidarity between peers and the improvement of behavioral regulation and order consciousness. Also, the experience of positive interactions followed by an efficient response as a member of society improved their social skills such as problem- solving and confidence by developing their abilities related to understanding others and engaging in interpersonal relationships. The study is significant to provide basic clinical data for improving the sociality of preschoolers by using ETC.