This study explored the effects of technology-mediated task-based language teaching (TMTBLT) in an English as a foreign language (EFL) writing course on students' descriptive writing performance. A quasi-experiment was conducted. Students in two writing courses were recruited and randomly assigned to an experimental or control group. The participants in the experimental group were engaged in the technology-mediated writing task of transforming their descriptive writing assignment, in which they introduced local tourist attractions, into videos to exchange online with foreign virtual peers. A mixed-methods research approach was adopted to analyze the data collected from participants' compositions and self-reflections. The results revealed that TMTBLT was effective in developing EFL students' descriptive writing proficiency. In addition to improving their writing, the students enjoyed participating in the task and used multiple skills. The implications of this study for TMTBLT in EFL writing teaching practices are also discussed.