This study analyzed the text readability of the College Scholastic Ability Test (CSAT) and High School English Ⅱ textbooks by focusing on reading and compared the difficulty levels between them. To analyze the readability, the Flesh 2.0 for Windows and the Web VP 1.5 (2003) were used. To find out about high school students’ attitudes and behavior towards English and their preferences of English books, a questionnaire consisting of ten questions was administered. The results revealed that the textbooks are more readable than the CSATs in terms of the Flesch-Kincaid Reading Grade Level (RGL) and Reading Ease Score (RES). The average length per sentence of the textbooks is shorter than that of the CSATs. Furthermore, the CSATs have a higher percent of academic words than the textbooks. The questionnaire results showed that the participants, 228 second-year high school boy and girl students, preferred CSAT prep books, followed by EBS books and textbooks. Based on the findings, the basic directions of the CSAT and the guidelines to write textbooks have been suggested.