Code switching has been used as a teaching strategy in EFL classroom to provide students’ comprehension of target language and its effects on students in learning English is still being discussed by experts and researchers. This research was conducted to investigate code switching used by English lecturers at Department of English Education at UIN Ar-raniry. The aim of this research is to determine the factors influencing lecturers to use of code switching in teaching EFL and also the effects of code switching on students in learning English. This research employed observation and questionnaires as the research instruments and the data were obtained from 2 English lecturers and 52 students. The study's findings indicated six factors that influence the use of code switching in EFL classroom, including translation, quotation, comprehension check, classroom management, clarification and asking students’ participation. The present study also revealed that the use of code switching upgrades the lesson more understandable, improves students’ vocabulary and increases motivation to participate in classroom activities. This study concludes that code switching can be a highly useful method in order to improve the effectiveness and enjoyment of teaching and learning in an EFL classroom.