This study aims at investigating code mixing and code switching found in the speaking class used by the teacher. this research is focused on the forms of code mixing and code switching; the frequency of the use code mixing and code switching; and the reason which underlie the teacher decision to code mixing and code switching in the speaking class. The research design of this study is descriptive qualitative. any figures in the form of precentages are not simplified into judgements. Instead, they are discussed, analyzed, and explained using a qualitative approach. The sources of the data for this research are the speaking teacher. The type of the data in this research is teacher utterances which contain code mixing and code switching. There must be acceptable procedures and methodologies used in conjunction with language teaching in schools. Teacher can instruct students using either code switching or code mixing, two different teaching strategies. When teachers teach in full English, not all students can grasp what the teacher explains, and pupils will be quiet and inactive. Code switching and code mixing are techniques to help students understand teachings. Students will participate by employing code switching and code mixing since everyone can comprehend what the teacher is saying. As a result, classroom activities are beneficial because teachers and students can communicate. The researcher is interested in learning more about the phenomenon of code mixing and code switching in the teaching and learning process, which departs from the issues and theories discussed above. The descriptive qualitative methodology used in this work strives towards descriptive analysis, necessitating the necessity for various forms of descriptions. The teacher's speech serves as the research's source of data, and it was collected using three different methodologies. Specifically, observation, discussion, and documentation. This study found the reasons for code mixing and code switching by the teacher in the speaking class. Then, this study also found differences in the frequency of code mixing and code switching used by the teacher in the teaching and learning process in the speaking class when he explained the material and gave instructions. The results it can be concluded that there are Intra-sentential of Code Mixing and Intra-sentential of Code Switching found in this study. The teachers speak although their mastery of English is very good, as native Indonesian speakers. Therefore, it is natural that the influence of their mother tongue is still very strong. Teachers use code mixing and code switching when they realize that students do not understand or are confused by what the teacher is saying.