The purpose of this study was to investigate the possible effects of conducting regular collaborative activities via Google Docs on English academic writing skills. Utilising a mixed methods design, this study was conducted with 24 Vietnamese high school students who participated in a fully online English as a foreign language (EFL) course in academic writing. The pre- and post-test results indicated that the students' overall academic writing skills were significantly improved over the course. Regarding individual aspects of academic writing, there were significant improvements in the areas of task response and lexical resources, while the areas of cohesion and coherence and grammatical range and accuracy did not witness significant improvements. Further analysis of semi-structured interviews with these students revealed that they valued the usefulness of Google Docs-based collaboration in enhancing their English academic writing skills, however they held mixed opinions about the enjoyment of collaborating on the platform. This study also revealed a number of challenges experienced by this group of students when they used Google Docs in online collaboration. Implications and suggestions for future studies are discussed.