This study aimed to investigate EFL students’ challenges in writing their undergraduate thesis by identifying internal and external factors that hindered students from finishing their thesis and exploring the strategies used by students to deal with their difficulties. This research employed a mixed-method design. The participants of this study were fifteen EFL students from the English Language Education Department batch 2017 at Islamic State University of Ar-Raniry. The participants were selected using random sampling. The researcher used questionnaire and interview as instruments to gather the data. The results of this study showed that paraphrasing sentences and paragraphs was perceived as the most challenging aspect among other internal factors. On the other hand, students faced difficulties in finding relevant materials or sources, which served as an external obstacle for English department students in writing their thesis due to the limited resources available on the campus. To address these complexities in thesis writing, students employed various strategies to overcome the challenges, such as setting priorities, managing their time effectively, maintaining consistency, and increasing their motivation.