Language is the main tool to make interpersonal communication in the society. This aim of this study is to describe interference forms in form of regional languages into Indonesian language that is used in the formal communication of Indonesian language learning. Using of qualitative method, the first step is to make a research by using of a write-record technique, making of data transcription, collecting of data according to types of interference, analyzing of interference forms as well as elucidating of contributing factors of interference. Results show that there weresome students who still interfereIndonesian language with their regional languages in the formal communication of Indonesian language learning. Language interference in this study classifies in three investigations – Phonology, Morphology, and Lexical. Interference in the formal communication caused by several factors; background, intimacy and prestige made by a speaker. Background factors of regional language interference into Indonesian language in the Indonesian language learning are understanding of second language, understanding of structure, verb composition, mastery of vocabulary, and inappropriateness in words choosing.