This study sought to examine the mediating roles of three dimensions of commitment (continuance commitment, normative commitment, and affective commitment)—key concepts of customer relationships in relationship marketing—and identification, a concept considered important as a psychological bond among members in membership relationships, in investigating the influence of online membership characteristics on customer loyalty. To achieve the purpose of this study, data were collected and analyzed from free online membership subscribers of a mobile telecommunications company, an offline firm with a relatively well-established online membership program. The results of hypothesis testing are as follows. First, in analyzing the effects of membership characteristics on the three dimensions of commitment and identification, the duration of online membership enrollment had no effect on any of the three dimensions of commitment or identification, while higher frequency of access and longer access duration were associated with higher levels of continuance commitment, affective commitment, and identification. However, actual participatory activities, which were expected to exert a strong influence, were found to affect only normative commitment. Second, the mediating variables of affective commitment, normative commitment, and identification were found to influence customer loyalty toward the offline firm.