Research writing is an important part of doctoral study. Previous studies suggest that students who speak English as an additional language (EAL) may experience difficulties in writing a thesis in English. This study investigated the nature of the writing challenges experienced by EAL doctoral students. Drawing on data collected from individual semi-structured interviews with 27 EAL doctoral students in various disciplines at an Australian university, this study found that while many participants encountered linguistic challenges and socio-cultural challenges, some participants thought that native speakers also faced challenges in academic writing. Major linguistic challenges reported were over-reliance on translation and L1-L2 rhetorical differences. Additional challenges included lacking local learning experiences, difference in learning expectations, and social isolation. This study has practical implications for curriculum design of language support services for doctoral students and training programs for supervisors. It concludes with recommendations for students, supervisors, and academic literacy professionals.