Recently many companies build interfirms cooperation based on their trust. These typology of partnerships play important roles for good results especially for joint product development. Therefore the purpose of this article is to investigate the role of interfirms communication in B2B market. We also investigate interfirms communication affecting the result of new product performance through two relationship factors(trust, conflict) in B2B market. Data were gathered from respondents who work in industrial buying center. Major findings of this study are summarized as follows: First, communication has positive effects on trust but negative effects on conflict. Second, trust is shown to have positive effects on cooperation and new product performance. However, conflict is shown to have negative effects on cooperation and new product performance. As a result, interfirms communication derives new product performance. In conclusion, this study means that we tried to investigate the human relationship in B2B market.