This research aimed to know the types of code switching and the reasons of using code switching by teacher in teaching learning process at SMPN 34 Samarinda. The research method that used in this research was descriptive qualitative method by applying naturalistic design. The subject of this research was English teacher at SMPN 34 Samarinda. This research used observation and interview to collecting data. The result showed there were three types of code switching that used by English teacher in teaching learning process, namely intersentential code switching, intra-sentential code switching and extra-sentential code switching/ tag switching. Inter-sentential code switching was the dominant type that use by English teacher. There are 27 utterances included inter-sentential code switching, 14 utterances included intra-sentential code switching and 2 utterances include extra-sentential code switching/tag switching. While the reasons of the teacher used code switching in teaching learning process were first, the student's English proficiency were in low level, especially in 7th grade. That is why the teacher switch the language from English into Bahasa Indonesia to avoid
misunderstanding during teaching learning especially in giving instructions. Second the teacher used code switching to facilitate the comprehension in teaching learning.