Reading has been an important language skill and many reading instructions have been explored in order to enhance the development of reading proficiency. In particular, extensive reading has been widely adopted and found as an effective reading instruction because it creates an input-rich context through providing a great amount of reading. However, it was pedagogically challenging to prepare a wide variety of books classified according to reading/language proficiency for EFL learners and to match students’ reading/language proficiencies with books of corresponding reading/language proficiency. Therefore, the present study aimed to examine the effect of extensive reading incorporated the Lexile framework, which offered measurements and books with corresponding reading proficiency, and the students’ perceptions were examined. In this study, a pre- and post-test design was adopted and sixty-six students were invited to participate in the experiment for two semesters and they were required to take Lexile measurements, conduct extensive reading for a minimum 3,000 pages, complete book reports as a post-reading activity, and fill out a survey. The researcher’s field notes were also included to triangulate the qualitative data analysis. The results indicated that the students have significantly improved, suggesting that extensive reading incorporated Lexile framework was effective in enhancing students’ reading proficiency. The results showed students’ positive attitudes and difficulties for extensive reading. Pedagogical implications were suggested.