Associate Professor, Dept. of Business Administration, College of Business and Economics, Yonsei University** Ph. D. Candidate, Dept. of Business Administration, College of Business and Economic, Yonsei University攀攀The purpose of this case study is to find out which factors of Daum Communications of successful business model and business strategy that plays an important role as the best internet company. Therefore, the study investigates the growth of Daum Communications by separating three period from business model, marketing strategy, financial strategy, HRM, and IT of viewThis case study has found that Daum Communications execute the rapidly transformation of business model to cope with changing situation. Specially, so far, Daum Communications continuously keep on competitive advantage as internet portal site through building core competence. that is, Daum Communications take into consideration such capability-related factors as strategic alignment with business strategy and financial strategy, corporation culture as 'horizontal network', IT resource management as in-house developing e-mail system. and Daum continuously expand customer contact points and open a new ground level of Internet business, to provide the most effective marketing platform in Korea, to solidly shape its position as the best Internet company.This study shows that Daum Communications's case broadly apply reference model to the building business model and formulating business strategy with internet portal service and other internet business models. Finally, we intends to discuss about theses questions. the question is "by the existing state of entering SK Telecommunication in wireless internet service, Can Daum Communications have sustainable competitive advantage in internet portal?", and "what is Daum Communication's next business model?".