The quality of a textbook might have fundamental roles that it can determine the success or failure in teaching and learning course. The present study evaluated English textbooks used in Iranian high schools, which are claimed to have been published based on the components of Communicative Language Teaching (CLT) approach. The purpose of this study was to explore high school teachers’ and students’ attitudes towards the Iranian high school English textbooks. To fulfill the objectives, a questionnaire consisting of 45 questions related to high school English textbooks was administered to 150 male and female high school students and their teachers in Isfahan, Iran. The participants were also interviewed in terms of their attitudes towards CLT and its implementation in Iranian high school English textbooks. The descriptive analysis of the data indicated that Iranian teachers and learners in Isfahan had a positive attitude towards the English textbooks based on the CLT principles. The majority of participants stated that 80 percent of CLT principles were currently practiced in Iranian high school English textbooks; however, some changes might improve the quality of these English textbooks.