The present study aimed at examining the effects of English collaborative writing and learners’ reflections on the experience of collaborative writing. The study was classroom based, and the participants (n=33) were Korean graduate students majoring in English education. The study compared texts produced by pairs (n=22) with those produced by individuals (n=11). Among the participants, nine students, involving the collaborative writing, participated in the follow-up interview. The study found that collaborative writing had an overall significant effect on students’ L2 writing. In particular, pairs produced better texts in terms of content, organization, and vocabulary, but not grammar and mechanics. The results of the student interviews showed that collaborative writing helped them pool ideas and provide each other with useful feedback. Most students were positive about the experience while a few of them demonstrated some reservation about collaborative writing.