This study examines the extent of L1 (Arabic) use by Saudi EFL lecturers in undergraduate lectures and delves into the underpinnings of L1 functions in these lectures. Four Saudi university lecturers (two males and two females), who teach undergraduate courses, at the College of Language Sciences at King Saud University participated in this study. Thirteen lectures in the courses: English Teaching Methods, Semantics, CALL and Research Methods were audio-recorded and each one lasted between 50–100 minutes. Ferguson’s (2009) theoretical framework for the functions of classroom code switching was adopted to analyse the data. The results revealed that although all lecturers switched codes, it was quite limited as the mean of the number of L1 words was only 4.83%, and the mean of the code-switching frequency was 25.76%. Additionally, two main functions of L1 use were found in the lectures: the construction and transmission of knowledge and the establishment of interpersonal relations.