The purpose of this study was to understand (1) countertransference experiences and changes on therapeutic attitudes of play therapists-in-training, (2) countertransference management process through supervision, and (3) clients’ therapeutic progress. A qualitative descriptive case study design was utilized, and two therapist-child dyads were recruited. Perceptional change of therapeutic attitudes was assessed weekly with the BLRI(Form MO-40), and the data was analyzed through visual analysis. The 12 weeks of play therapy video clip, play therapy practicum report & session summary, play therapy skills checklist, and interview data were qualitatively analyzed. Both play therapists-in-training perceived the trend of their therapeutic attitudes increased while the variability fluctuated. The process of countertransference management ability was analyzed, and clients also exhibited progress through the course of play therapy. The findings suggest some implication to promote professional development of play therapists-in-training.