This research is aimed to explore the challenges faced by EFL undergraduate student during the thesis writing process, language learning strategies used by EFL undergraduate student during the thesis writing process, and the way EFL undergraduate students construct new understandings about the topic of the thesis. This research employed biographical narrative inquiry. The data was collected by using semi-structured interviews and document analysis. The data was analyzed using thematic analysis. The result shows that the participant faced several challenges in writing the thesis namely difficulties in writing using appropriate grammar and content, choosing correct theories, and presenting data. The participant used four types of language learning strategies during the thesis writing process, namely cognitive, social, metacognitive, and affective strategies. In terms of new understanding construction, the participant constructed new knowledge starting with autonomously reading the resources related to the topic of the thesis, asking for the consultant and peer’s scaffolding in the form of feedback and discussion session, and it resulted in the new understanding of politeness strategy, critical thinking, and self-correction skills.