Textbooks are essential resources for both learners and teachers when teaching Turkish as a foreign language. Texts in textbooks are the most fundamental documents used to instruct foreigners in Turkish. Texts in textbooks should be appropriate for the student level in terms of a variety of characteristics. Readability is one of the characteristics cited in the literature for determining the appropriateness of textbook texts to the student level. This study analyzed the text readability levels of the Anahtar-Turkish for Foreigners C1 textbook. Document analysis was utilized in the data collection process of the study. Two different formulas were used to determine the readability of the texts in the textbook: the Ateşman and Çetinkaya-Uzun formulas. The data were descriptively analyzed. The texts were categorized according to their levels of difficulty, and the results were tabulated. The study concluded that according to both formulas, the readability levels of the texts in the Turkish for Foreigners C1 textbook are similar; the texts are at a medium level according to Ateşman and an educational level according to Çetinkaya-Uzun, and the related textbook is easier in terms of readability level than similar textbooks in the literature.