This study was conducted to investigate the effects of behavioral skills training on conversational skills in adults with developmental disabilities. Two adults with developmental disabilities who had difficulties interacting with others due to a lack of appropriate conversational skills participated in the study along with one of their colleagues with appropriate conversational skills, who participated as a norm. Behavioral skills training was implemented to improve the conversation skills in the participants, and the effects of the intervention were evaluated using a multiple baseline across participants design. The experiment consisted of baseline, intervention, maintenance, and generalization during each experimental condition. The results indicated that the conversational skills of the participants were improved with the behavioral skills training, and the acquired conversational skills were maintained even after the intervention was removed. In addition, the generalization effect was observed when talking to other who did not participate in the intervention. The social validity evaluation by the participants, their parents, and their supervisor showed very positive results, and two participants indicated a similar or higher level of conversational skills than their colleague, which was the norm.