This study explores undergraduates' attitudes toward extensive reading (ER) and reading graded readers online via Xreading.com in a large-scale ER program (ERP) involving over 5,000 students. Data were obtained from 356 students via an online questionnaire and 13 students in three focus groups. The quantitative findings showed that the students had positive attitudes toward ER. The top three reasons included (1) reading graded readers made them enjoy reading in English more than before, (2) they were more motivated to read graded readers because the stories were simple, and (3) they preferred to read shorter texts because they were simpler. Additionally, the qualitative findings revealed that all 13 students enjoyed freedom of choice in which they could choose their own graded readers that matched their interests and proficiency. Also, students had positive attitudes toward online ER through Xreading due to a variety of graded readers, an opportunity for students to practice their English and reading skills, enjoyment from reading, convenience and ease of use, and self-monitoring features. However, two difficulties were reported, including not knowing which graded readers to choose and eyestrain when reading online. Finally, pedagogical implications are discussed to guide ERP coordinators and teachers.