The study was designed to investigate how collaborative writing techniques influence on English writing products of Korean college students and the improvement of their English writing abilities, compared to an individual writing opportunity. 54 college students (48 Korean students and 6 international students) taking two parallel in-tact English composition classes offered by a national university participated in this study. The participants, depending on which section of the writing course they registered, were asked to work on writing an English essay either collaboratively or individually, as three writing phases, pre-, during-, and post-writing step with a variety of activities, proceeded. Three major research instruments (students` written texts, survey, and interview) were employed to answer three research questions on the contribution of collaborative writing to their English writing improvement. The findings were that collaborative writing techniques were helpful for EFL college students not only to achieve knowledge of English, in particular, usage of grammar and punctuation but to develop their communication skills and English writing strategies even though the study failed to demonstrate that students writing their essay collaboratively produced better written texts than those writing individually. Lastly, pedagogical implications for college English composition courses and suggestions for future studies were also provided.