The aim of this study was to know the types of code mixing usage in conversation and the reasons behind the use of code mixing. This study was conducted to observe and analyze from the interaction in the class. The method in this study was a descriptive qualitative research where the researcher used a description table as data because the researcher was required to examine the data from the conversation and properly explain the results of the data that had been collected. In this study, there were 3 types of code mixing used, namely insertation, alternation, and congruent lexicalization. Based on the data, there were 179 uses of code mixing in dialogue, 54 dialogues using insertation, 90 alternation and 35 congruent lexicalization. Code mixing occurred for several reasons, namely bilingualism, speaker and partner speaking, social community, situation, vocabulary, and prestige. The researcher also found out the reason why code mixing accourred in the conversation”. There are six reasons why code mixing happened they are bilingualism, speaker and partner speaking, social community, situation, vocabulary and prestige.