This study explores whether an extensive reading (ER) approach can enhance L2 learners’ writing performance in an English for Academic Purposes context. Two classes were compared in terms of writing improvement after one semester: a ‘traditional’ writing class primarily focused on writing practice and grammar instruction, and an ER class in which students engaged in ER in and out of class, along with completing reading-related writing activities. Essay tests were administered at the beginning and the end of the semester to measure students’ writing improvement. The study found that although both classes demonstrated writing improvement after one semester, students who were exposed to more input through ER gained significantly higher holistic scores in their post-essay test. In addition, analytic evaluation found that the ER class improved more than the traditional class in the specific areas of content, organization, vocabulary, language use, and mechanics.