This study investigated the effects of online collaborative writing and writing contributions in Google Docs of 35 Asian EFL university learners in a composition course. Data were collected from students’ pre- and post-test writing, two extended online collaborative tasks: writing descriptive and argumentative essays, and student reflections. Students’ writing performances were assessed using Jacobs et al.’s (1981) composition analytic scoring rubric. Paired sample t-test analysis showed that academic writing performance significantly increased after participating in two extended collaborative writing tasks. Learners developed more extended written texts and texts were more accurate in the post-test writing. Furthermore, Pearson correlation coefficient (Pearson’s r) analysis showed that learners’ text contributions, their use of writing change functions and language functions during the collaborative process was positively correlated with their post-writing performance. This study supports the notion of writing as an exploratory and recursive process, but not linear.