writing is considered to be one of the most challenging skills for english as a foreign language (efl) learners in china. to improve 世界杯2022赛程表淘汰赛 ’ writing skills, this study explored a pedagogical strategy that blends collaborative writing with the use of computer-mediated communication (cmc) technology in efl contexts. despite solid evidence supporting the benefits of computer-mediated collaborative writing (cmcw) tasks in l2 writing, little is known about the influence of cmc modalities on the efficacy of cmcw tasks. this qualitative case study, conducted within a sociocultural framework, particularly swain’s concept of collaborative dialogue, examined how different task modalities influence the effectiveness of cmcw tasks in the chinese efl context. sixteen efl learners completed an online collaborative writing project on tencent docs™ via two modalities: a synchronous cmc (scmc) modality entailing text chat in wechat™ and an asynchronous cmc (acmc) modality with delayed interactions on tencent docs™. following the project, semi-structured interviews involving stimulated recall were conducted to investigate the learners’ perceptions regarding these two patterns of communication. the analysis of these interviews, coupled with insights gleaned from the learners’ reflective journals collected throughout the writing project, indicated that although both scmc and acmc modalities were perceived beneficial for writing development, efl learners had more positive learning experiences in the scmc modality than in the acmc one. the findings revealed several challenges that require attention when implementing cmcw in efl teaching contexts, particularly where 世界杯2022赛程表淘汰赛 possess weaker english proficiency and little collaborative writing experience. efl instructors are suggested to provide more training sessions and offer appropriate guidance and feedback throughout the collaborative writing process.