Not many readability studies have been carried out on Indonesian language textbooks for foreign speakers (BIPA). This study analyzes BIPA Sahabatku Indonesia textbooks' readability at B1 and B2 levels through fog index. The research method used is the descriptive qualitative method. Data collection was carried out using documentation techniques on discourses in the BIPA Sahabatku Indonesia textbook published by the Ministry of Education and Culture in 2016. According to the fog index criteria, this research is used as teaching materials for reading skills, namely eight lessons in textbooks B1 and eleven lessons on B2. Data were analyzed using measurement techniques through the fog index formula developed by Gunning. Based on the fog index, level B1 textbooks had a mean score of 2.98 with elementary criteria, while B2 level textbooks had a mean score of 4.02 with easy standards. Thus, as a representation of the existing BIPA textbooks, the intermediate level Sahabatku Indonesia book, both B1 and B2, shows less ideal criteria.