Slang is one of language variation. It consists of word, phrase and sentence that related to informal interaction and used in informal situation. The aim of this study are to find out the types of slang used by the lecturer and the students, the factors causing the use of slang, and the reasons of using slang. This study used qualitative descriptive method to collect the data from the lecturer and the students of English Education Department in University of Muhammadiyah Luwuk. To collect the data, the researcher observed and recorded all conversation in the classroom and also used interview for getting the data from the lecturer and the students.
The findings show that the lecturer and the students employed fresh and creative type, compounding type, imitative type, and clipping type in communicating in the classroom. The result of the analysis also shows that social status, age, social distance or familiarity and situation are the factors that affecting the use of slang in the classroom. Moreover, the participants also revealed the reasons of using slang, they are to reduce seriousness, to induce either friendliness, for ease social interaction, to enrich the language, to be different, for the delight, to imitate and joke.