Abstract-This study investigates senior high school students' reading comprehension of graded readers outside of the classroom. Seventy-eight participants were assigned to read three graded readers written respectively from 600-word, 1200-word, and 1700-word wordlists and labeled as Level 2 (L2), Level 3 (L3), and Level 4 (L4). All participants completed post-reading comprehension tests, follow-up reading tests, and post-reading questionnaires. T-test results showed that first, females' reading comprehension ability had grown significantly. Second, there were no significant differences between males and females' comprehension of L2 and L3 readers, but females achieved significantly higher scores than males in L4 graded reader. Third, females significantly used more strategies than their counterparts to understand L4 graded reader. Finally, the interpretation of females' adding and reducing the strategies to comprehend difficult text were provided. Instructional suggestions for senior high school students' outside reading were presented.