This study evaluated the third-grade junior high school English course book in Iran which was implemented in 2017 by the ministry of education. The study was done in order to find out whether its contents match the authors' claim. To do this, the researcher used a quantitative research design to evaluate the Course Book (CB). A sample of 200 teachers participated in this study for answering the questionnaire and were chosen randomly from a different state and private schools in Mazandaran province. They participated in the online and paper and pencil survey. The survey was developed by Cunnings Worth (1995). The items of the questionnaire were based on the characteristic of a good textbook and included 14 categories as content, grammar, vocabulary, phonology, language skills, methodology, study skills, objectives, content selection, gradation and recycling, visuals, practices and testing, supplementary materials and teacher manual. In short, the results indicated that Prospect 3 was perceived as moderately adequate since the mean composite scores for each category exceeded 2, except for gradation and recycling which scored 2.10. Gradation and recycling and study skills categories were two categories that scored a mean of 2.13 and 2.10. They gained the least support by the respondents. پرونده مقاله