ABSTRACT: Word formation in Indonesian is one of the important processes because it will give meaning. In the Indonesian language, the process of word formation is studied in depth in the study of morphology. Indonesian Language for Foreign Speakers, commonly referred to BIPA, is one part of Indonesian language learning. This study describes the errors that exist in the writings of BIPA learners at IAIN Surakarta, which specifically discusses the morphological errors in affixation, reduplication, and basicword writing errors. This study is a qualitative descriptive study with a single case study. The main data sources in this study were the documents written by BIPA participants in IAIN Surakarta. The analysis technique used in this study was an interactive analysis technique, which includes activities to analyze the data on the application of actions in learning consisting of four main components, namely, data collection, data reduction, data presentation, and conclusion drawing or verification. Based on the results of the study, it can be concluded that there were eight errors that occurred in the writings of BIPA participants in IAIN Surakarta. First, the error is in the affixation process in the forms of prefixes me-, ber-, suffix -an, and confixes ke-an, me-an. The second error is in the reduplication process and the third in writing basic words.
KEYWORDS: error, morphology, BIPA