This research aims at finding out code mixing and code switching in the classroom interaction in terms of the teacher talk and the student talk at SMP Negeri 2 Parepare. In detail, this research aims to identify (1) the teacher talk particularly the type token ratio, the mean length of utterance as formal features, question, feedback and correction as interactional features, (2) the students talk particularly response to question and ask question as well as the students’ preference towards the use of code mixing and code switching the students in learning achievement. The research employed mix method research design. The subjects consisted of the teacher and the students. There is 1 teacher and 81 students which are divided into three classes. Each class consists of 27 students. The research data were collected by non-participant observation which was analyzed by using formal features, interactional features, descriptive and inferential statistics through SPSS 21.0. The research result indicated that (1) the type token ratio in code mixing and code switching Indonesian/English in classroom interaction varied. It reveals that the vocabulary used by the teacher varied, (2) the speech of the teacher when addressing the students in the classroom by mixing and switching the language contained longer utterance, (3) the teacher used convergent and divergent questions in mix and switch the language when addressing students in the classroom interaction, (4) the teacher provided interactional corrective feedback and correction in mixing and switching the language when addressing students in the classroom interaction, (5) there are three reasons why the teacher mix and switch the code in the classroom interaction namely to give clear explanation to the students, to make the students easy to understand, and make the teacher and the students close to each other, (6) There are two types of students in response to the question namely the role of students to the teacher (S-T) and the role of students to students (S-S) in code mixing and code switching in the classroom interaction, (7) there are two types of the students question in code mixing and switching of Indonesian/English when asking the teacher namely procedural questions and convergent questions, (8) the students’ preference towards the use of code mixing and code switching in the students learning achievement consist of two main points in this research namely, first the use of code mixing and switching convince positive attitude and second positive role to the students preference towards the use of code mixing and switching the students in learning achievement.