The purpose of this single-case experimental design (SCED) study is to investigate how adaptive prompts in virtual reality (VR)-based social skills training affect the social skills performance of autistic children. Adaptive prompts are driven by autistic children's emotional states. To integrate adaptive prompts in VR-based training, we conducted speech data mining and endorsed micro-adaptivity design. We recruited four autistic children (12-13 years) for the SCED study. We carried out alternating treatments design to evaluate the impacts of adaptive and non-adaptive prompting conditions throughout a series of VR-based social skills training sessions. Using mixed-method data collection and analyses, we found that adaptive prompts can foster autistic children's desirable social skills performance in VR-based training. Based on the study findings, we also describe design implications and limitations for future research.