This research investigated the use of code mixing by the teacher in English teaching learning at the seventh grade of SMP Perjuangan Prambon. The study aimed 1) to describe the types of code mixing used by the teacher in English teaching learning process in language class the seventh grade of SMP Perjuangan Prambon. 2)to describe the students’ perception on code mixing used by the teacher in English teaching learning process at language class the seventh grade of SMP Perjuangan Prambon. This research applied descriptive qualitative design. The data was taken from the classroom by observation during learning process and to obtain the data regarding students’ perception toward code mixing that the teacher used, the researcher used questionnaire. The data was analyzed based on the types of code mixing by Hoffman’s theory. The results showed that there are three types of code mixing consisting of 99 utterance (data), 77 data of intra sentential code mixing, 12 of intra lexical code mixing and 10 of involving a change of pronunciation. For students’ perception, 86% students from 14 students are interested in the using code mixing by teacher in English teaching learning process is necessary to help them understand the content and the teaching learning process can run well.