The formation process of electronic communities on WWW bulletin boards was observed for 6 months. Subjects were 106 Internet users were unacquainted with one another. They communicated freely on a WWW bulletin board. Based on time course change of the number of remarks, participants were classified into 3 groups; high-participation group, low-participation group, and early high-participation group, members of which made remarks only in the early days. Compared with the other groups, subjects in the high-paticipation group tended to more frequently use the network for sending information (e.g. making remarks on Netnews), and had higher communication skills, which formed a sub-structure of social skills. The results suggest that social skills were related to active participation in electronic communities.