This paper intends to identify the correlation between ER and students’ critical thinking. The participants of this research are the first-year students of English Education study program in Universitas Negeri Surabaya who take part in ER program. The ER program implemented for students is X-Reading, an online extensive reading website with learning management system (LMS) that provides hundreds of graded readers. The data are collected from the recorded time spent by students on X-reading activities and questionnaires based on students’ perception on how extensive reading contributes to their critical thinking skill. The data are analyzed using Product Moment formula and Coefficient Determination to find out to which extent X-Reading contributes to students’ critical thinking skill.