This research aims to describe the dynamics of social identity formation in the CB Constant motorbike community through interpersonal communication, this community is in the city of Pacitan. The theory used is the 3 dimensions of the social identity process which was initiated by Henri Tafjel. The method used was descriptive qualitative with 12 informants who had been determined by the researcher. Arif Sugiyanto, chairman of the CB Constant Pacitan community, eight members of the CB Constant community, local residents and members of the Pacitan traffic police. The research results reveal that members of the CB community constantly form social identities because of their interests and hobbies. Referring to Henri Tafjel's theory, it uses 3 dimensions, namely social categorization, social identification, social comparison. After conducting observations and interviews, the CB Constantan Pacitan community has fulfilled the 3 dimensions well. The CB Constant community plays an important role as a forum for the process of forming the social identity of its members.