Muhammadiyah University of Malang (UMM) is one of private universities in Malang. Its students come from many places in Indonesia. This phenomenon makes the languages that they are used vary. Mostly, in their daily conversation they use Indonesian and Javanese. Sometimes, they use Slang language that appears unique and funny in their daily casual conversation usually called “Bahasa Gaul” (“Gaul” language). The problems that will be discussed are:(1)What parts of speech are used in “Gaul” language spoken by students of UMM? (2)What are the characteristics of “Gaul” language used by students of UMM? (3)Why do they use “Gaul” language? and (4)With whom do they use “Gaul” language?.The objectives of the study are to know the parts of speech of “Gaul” language used by students of UMM, the characteristics of “Gaul” language used by students of UMM, the reasons why they use “Gaul” language, with whom they use “Gaul” language.In writing this thesis, the writer used descriptive qualitative method because she just described “Gaul” language used by students of UMM based on the phenomenon. The writer got the data by interviewing and giving some questionnaires to the informants. Besides, she also used documentary. Next, the writer analyzed the data in several steps.After analyzing the data, it is found out that: (1) parts of speech of “Gaul” language can be classified into: Noun, Pronoun, Adjective, Verb, Adverb, and Interjection; (2)”Gaul” language has some unique characteristic as a secret language, an informal language used by young people and a developing language in term of new vocabularies; (3)”Gaul” language is used for telling a secret, having fun, creating familiarity, being exclusive and being acceptable in their friend group; (4) The speakers of “Gaul” language are young people. Students of UMM use this language with their friends but they sometimes use it with their siblings and relatives.