Background: The present study is aimed at investigating the relationship between changes in symptoms and changes in social functioning during cognitive behavioral therapy (CBT) for social anxiety disorder (SAD). Methods: Ninety-six patients with SAD were treated with manualized group CBT. Measures of social anxiety symptoms, depression symptoms, cognition, and social functioning were administered at baseline and endpoint. Using multiple regression analysis, we examined the associations between the changes in four aspects (work, home management, social leisure activities, and private leisure activities) of social functioning as dependent variables and the changes in four factors (social interaction, public speaking, observation by others, and eating and drinking in public) in social anxiety symptoms, depression symptoms, and cognition as independent variables. Results: The changes in work functioning were predicted by the changes in the public speaking factor in social anxiety symptoms. The changes in depression symptoms predicted the changes in home management. The significant predictors of changes in social leisure activities were the changes in the social interaction factor and depression symptoms. The changes in private leisure activities were predicted by the changes in the observation by others factor. The changes in cognition predicted nothing. Conclusion: The present study suggested that the changes in social anxiety or depression symptoms may predict several aspects of social functioning changes in patients with SAD over the course of CBT. In order to improve social functioning, our results may be useful for selecting the fear or feared situation in CBT for SAD. Trial Registration. The clinical study registration number in the Japanese trials registry is UMIN CTR 000031147.