The purpose of this study is to investigate the challenges that EFL learners at Van Lang university faced when they learned writing in an online course via Microsoft Teams. 96 third-year students from two classes were required to complete a 10-item questionnaire for their online 10-week writing course. The findings revealed that they faced nine kinds of challenges related to technical problems, lack of concentration, lack of interaction, time management, health problems, gaining knowledge, motivation, psychological problems, and collaboration. The study suggests some implications for teaching writing skills to EFL learners online through Microsoft Teams.