The present study aimed to examine the moderating role of the quality of the relationship between children and their teachers (i.e., closeness and conflict), in children’s unsociability and play behaviors (i.e., reticent behavior, social play). Participants were 211 three- to six-year-old children (M = 64.08 months, SD = 10.92, 94 girls, 117 boys). Mothers reported their unsociability; teachers reported teacher–child relationships and children’s play behaviors. Results showed that close teacher–child relationships moderated the association between unsociability and social play in children (buffering effect). Teacher–child conflict exacerbated the relations between unsociability and reticent behavior. Findings show that teacher–child closeness is effective in revealing social play behaviors of unsociable children. Teachers can improve their relationship with unsociable children to provide nurturing social play behavior.