The purpose of this paper was to investigate the effects of mobile instant messaging on collaborative learning processes and outcomes. The collaborative processes were measured in terms of different types of interactions. We measured the outcomes of the collaborations through both the students' taskwork and their teamwork. The collaborative learning processes and outcomes in the Mobile Instant Messaging group (Mobile IM) were also compared with the Personal Computer-based Instant Messaging group (PC IM) and the Bulletin Board System group (BBS). A total of 48 students participated in this study, and the main results show that more cognitive and metacognitive interactions were found in the BBS group while social and affective interactions were the major types of interactions in the Mobile IM group and the PC IM group. As a result of the collaborative learning outcomes, the Mobile IM group shows better teamwork than the other two groups. However, better taskwork was found in the BBS group and the PC IM group rather than the Mobile IM group. Finally, the researchers discuss the implications of this study from the perspective of the educational potential of mobile learning.