The current study investigated the effect of synchronous computer-mediated communication (SCMC) on developing L2 learner utterance fluency. Twenty-two native Japanese learners of English engaged in a series of task-based communicative activities in pairs for 12 weeks using the text-chat function of Microsoft Teams. Although their pre/post performances were not statistically different, the comparison of their oral performance recorded before and after the text-chat activities suggested a slight improvement in fluency, particularly in terms of the pause behavior with mid to large effect sizes. We argue that SCMC could be a promising alternative tool for L2 oral fluency development.