The main aim of the study was to compare students’ and teachers’ perceptions about English Textbooks of Khyber Pakhtunkhwa Textbook Board for Intermediate Level, their contents and effects on students’ proficiency in English. The main focus of this study was to find out that as to what extents these textbooks cater to the language needs of the 11th and 12th grade students. Objectives of the study were (a) to analyze the perceptions of students and teachers about the English Textbooks of Khyber Pakhtunkhwa Textbook Board for class XI and XII. (b) to find out as to what extents these books are helpful in promoting students’ proficiency in English language. (c) to propose recommendations for further improvement in the existing English textbooks and teaching methods of teachers. The population of the study consisted of all the Intermediate level students and English Subject Specialists/Professors in Khyber Pakhtunkhwa. Data were collected from 1975 students and 108 English language teachers through pre-tested questionnaires one each for students and teachers in seven districts of Khyber Pakhtunkhwa. To analyze the difference between students’ and teachers’ perceptions about the English textbooks and their effects on students’ proficiency in English, independent samples t-test was applied. The results of the study showed significant differences in students’ and teachers’ perceptions about the textbooks and their role in affecting students’ proficiency in English.