The aim of this report is to review the utilities of "the two-step flow of communication hypothesis," and reflect on the modification process of this model. This model was, originally, generated from the study of voter's decision-making in the 1940 presidential campaign (by Lazarsfeld, Berelson and Gaudet). According to this hypothesis, "Ideas often flow from radio and print to the opinion leaders, and from them to the less active sections of the population". The two-step flow of communication hypothesis became a major stimulus for research-fields concerning the diffusion of information, influence and innovation. Many researchers tried to test this hypothesis, and they found that this model is too simple and clear. In reality, communication process is more complex and complicated than this model. In spite of some merits, for example, device of 'panel techniques', findings of 'opinion leader' as influencer, this model, undoubtedly, has some limits. This hypothesis is mainly tested in three research fields-mass communication research, study of social relations, and diffusion research. Later scholars pointed out that "Ideas does not always flow from radio, print and TV to the opinion leader (or equivalent), and from them to the less active sections of the population"