The purpose of this study was to investigate the effects of Pivotal Response Training on promoting communication skills for unconventional verbal behavior of child with developmental delays. This study utilized A-B-C of single-subject experimental design. The targeted participant received 60 minutes of intervention one or two days per week, and total was 10 weeks of intervention. The visual analysis, interobserver agreement, and procedure fidelity were used to analyze the outcomes of intervention, while social validity was implemented to understand whether such intervention meets the needs of targeted participant. The results revealed that was effective for the improvement of communication skills and social interaction, and the reduction of aggressive behaviors due to unconventional verbal behavior.