This study aims at defining the factors affecting adoption intentions for portable Internet services based on the characteristics of individuals creating the markets and developing strategies of the service, which is expected to be the next-generation telecommunication service. For this Purpose, two types of sub-factors are defined : characteristics of individuals including demographic statistics, usage of existing services, prior cognition, adoption attitudes and service assessments : and adoption Intentions including willingness for subscription, subscription period, willingness to pay, types of usage and preferred device. The results of the study indicate that demographical statistical variables vary depending upon the levels of adoption intentions, and that users of mobile Internet services via mobile phones and wireless LANs are highly probable of being targets for the portable Internet services. Furthermore, the results demonstrate demands for enhancing recognition of the usefulness and ease of use of the services and intense marketing activities for potential users bearing innovativeness to stimulate the market of the portable Internet service. The author is confident that this study will significantly contribute to the successful market entrance of portable Internet service, and also to growth in the market.