This study aims to explain the formation and reasons for the use of slang language of Pendalungan teenagers in Jember Regency. This research used descriptive qualitative method. The research data is in the form of words from Javanese and Madurese acculturation that contain slang language forms and spoken by teenagers in daily communication. Data collection used observation technique supported by listen-engage-note technique. The data analysis technique used is the commensurate (padan) method and the agih method. Based on the results of this study, there are four categories of slang variation formation in terms of morphological formation, namely: (1) Abbreviations, such as the abbreviation LA and the acronym Kardiman. (2) New Words, such as cungucui, pacapa, crème, and tompes. (3) Reduplication, such as ya megaya, and rep sekarep. (4) Inserts, such as cellepnya and ngabesnya. The reasons for using slang consist of five reasons, namely (1) familiarity, (2) solid and concrete, (3) user creativity, (4) group recognition, and (5) enriching vocabulary. The conclusion of the research findings shows the formation of slang language by absorbing Javanese and Madurese as well as new words that are different from the original language. Pendalungan teenagers in Jember district dominantly use slang language which is mixed with Javanese, Madurese, and Indonesian daily language.