The aim of this study was to examine how the role of graduate students differs when university professors participate in collaborative research. The study method involved the researcher interviewing three kindergarten teachers who had participated in various forms of practice research. The teachers were aware of four roles of graduate students. The following was shown as four roles. (1) Graduate students sympathize with teachers, and give them a boost by acting in an approving manner towards the teachers’ practice. (2) Graduate students supplement and explain the words of the university professors, leading them to act as intermediaries. (3) Graduate students give their opinions to teachers in a positive way. (4) Graduate students also take on a guidance role by supporting teachers. When university professors participated in the research, the graduate students took on an intermediary role between the university professors and the kindergarten teachers. However, the students tended to take on a stronger guidance role when the university professors were not present. In other words, the role of the graduate students changed in the presence of university professors. Therefore, the various roles adopted by the graduate students contributed to the success of collaborative research between teachers and researchers.