This study aimed 1) to explore Iranian EFL teachers’ attitudes towards the different aspects of the English textbooks prospectused at the first three grades of high school in Iran 2) to probe any relationship between the teachers 'attitudes towardsprospect series and their TKT level. A questionnaire and a structured interview were utilized as instruments in this research.The questionnaire was structured in 3 units: The first unit was intended to record the respondents’ demographic informationsuch as their age, sex, field of study, university, and teaching experience; the second unit including 24 items was intended todiscover the respondents’ level of TKT; and the third unit including 28 items was designed to elicit the teachers’ attitudestowards the current high school textbooks. This questionnaire of attitude was designed in the form of Likert scale includingstrongly disagree, disagree, slightly disagree, agree, slightly agree and strongly agree. The data of the study were collectedthrough administering the questionnaire to 80 teachers from Amol, Isfahan and Tehran. Also, semi-organized interviews havebeen carried out with twelve teachers selected from the eighty to cross-check the results of the study. Due to the rate of theabsence, seventy of them completed the questionnaire. After administering questionnaire, the data were analyzeddescriptively and inferentially. The results of the Pearson Chi 2 and Fisher's Exact p-value were respectively o.516 and 0.642. Since they are above %0.05, we can conclude that there is no significant relationship between Iranian EFL Teachers' attitudestowards the Book series ''Prospect'' taught in Iran's Schools and their TKT. The results indicated that a) the participants hadpositive (high) attitudes towards the English series Prospect b) There is not any significant relationship between the teachers’positive attitudes towards the new text books and their TKT level. Keywords: Iranian EFL teachers, attitude, textbooks, TKT.