Abstract :
This research is a Sociolinguistics study of code mixing that used by Yasmin, a 12 years immigrant child that lived in Batam. This research is aim to analyze the types of code mixing that argued by Hoffman and reasons of code mixing that argued by Hoffman and Saville Troike. The data was collected from an audio which contained the utterance of the 12 years old immigrant child. Then, the result of the data counted by using Walizer?s formula. The resulted show that there were seventeen data for the types of code mixing, and sixteen data for the reason of code mixing. For the types of code mixing, the highest type used is intra-sentential code mixing. While, the lowest type of code mixing used is intra- lexical code mixing. For the reason of code mixing that argued by Hoffman, the dominant reason of code mixing used is ?intetion of clarify the speech content for interlocuter?, while the reason of code mixing that aruged by Saville-Troike there were two dominants reason used, ?to soften or strengthen request or command? and ?because of real lexical need?. Code mixing used by the 12 years old immigrant child to make the communication runs smoothly and can be understood by the listener.