Abstract
This experimental research investigated the impacts of portfolio - based assessment on non -English majored students’ perception and their writing performance. The participants included seventy non -English majored students at Kien Giang University, who were divided into two groups including the experimental group and the control group with and without the intervention of portfolio – based assessment in their writing. The research instrument consists of writing tests (a pre - test and a post - test) and students’ portfolio to measure students’ writing performance, the questionnaire and the interview investigated students’ perception towards the implementation of portfolio – based assessment in writing classrooms. The results of the research pointed out that the experiment group had a significant improvement on writing performance. The participants in the control group also improved their writing performance, however, their improvement was less than that of the experimental group's. Finally, the suggested pedagogical implications are hoped to contribute to the innovation of assessment method in teaching writing in the context of Kien Giang University.