For some individuals with social anxiety disorders (SAD) comorbid with autism spectrum disorders (ASD), it is difficult to speak in front of others. Herein, we report the case of a patient with SAD comorbid with ASD who could not speak in front of others until she used a humanoid robot as her avatar. During the intervention, her personality changed from shy to outgoing, which is explained by the Proteus effect. These case findings suggest that interventions with a robot avatar might improve the motivation for individuals with SAD comorbid with ASD who cannot speak in front of others to communicate.