Study on Effectiveness and Group Communication Networks aims to understand the interrelationships effectiveness of communication with the communication network that is formed in the empowerment of farmer communities in the Lestari Makmur mushroom farmer groups in Argorejo Village, Sedayu District, Bantul Regency. This study use a qualitative-interpretive approach the case study method. The case study is a comprehensive description and explanation of the various aspects of an individual, a group, an organization (community), a program or a social situation (Mulyana, 2001: 201). The case studies are used when the phenomenon to be studied concerning the question how or why. Yin (2005: 9) illustrates the use of each of the research questions in the different studies. The case studies are used if little opportunity to control events were investigated and focused his research on contemporary phenomena. The results showed that, in particular a group communication for decision making in a mushroom farmer groups could form a communication network star, Y, triangle or a chain, with a tendency to farmer groups as a decision maker. Effective communication related to the communication network that is formed in the communication process. Each the problems solving in the group, has its own communications network so that the communication process runs effectively.