This study aimed to investigate whether there is any significant relationship between the readability and vocabulary profile including the most frequent words (K1 words) and academic word list (AWL) of reading passages of Four Corners series which were EFL textbooks. To determine the readability of the texts, the Flesch–Kincaid (1975) readability test was used, while the texts' academic word list and most frequent words which were the indicators of vocabulary profiler were calculated by Cobb's (2002) vocabulary profiler test. In order to analyze the data obtained Pearson Product-Moment correlation coefficients were exploited. With respect to the relationship between readability and most frequent words, there was no significant correlation between readability and K1 words. This means that whatever the text is more difficult, the number of K1 words does not change while it was thought if the text is more difficult the number of K1 words is lower. Concerning the relationship between readability and academic word list, no significant correlation between readability and academic word list was observed, either. In other words, the readability of these texts is not due to their academic word list. It can be concluded that some other factors such as sentence length, syntactic complexity, and learners' background knowledge might contribute to the difficulty of the texts. تفاصيل المقالة