This research was conducted to describe the kinds of preposition errors found in the students’ writing composition, to discover the kind of preposition errors mostly produced by the students, and to find out the sources of the errors. Since grammatical errors are considered the most common errors in students writing including in using prepositions, then the researcher attempted to analyze more specific grammatical errors, prepositions, in the students’ writing composition. This study applied descriptive qualitaive research design. The subject was the second-semester students of the English Department of Teacher Training and Education Faculty of University of Islam Malang. The researcher observed the 50 students’ descriptive text from two classes who were chosen using purposive sampling. The instrument used was the researcher herself as the main instrument who collected, analyzed, and interpreted the data. The researcher also used another instrument that helped the researcher to analyze, identify, classify, and interpret the errors which were some tables from Utari (2017). Based on the analysis, the data showed that the total preposition errors made by the students were 74 items where the errors of omission were 15 items or 20.2%, errors of addition were 14 items or 18.9%, errors of misformation were 44 items or 59.4%, and error of misordering was 1 item or 1.3%. Moreover, the preposition errors made by the students were caused by interlingual errors with 42 items, and intralingual errors with 32 items. Therefore, the preposition errors mostly produced by the students were errors of misformation which were mostly caused by their first language interference. The researcher could say that the students were lack of preposition mastery, so it made them applying their own rules for expressing their idea. Moreover, most of the students used incorrect prepositions in their sentences. In general, those errors were mostly caused by interlingual errors. Although this study was conducted at the university students level, this study proved that there were many university students confused in using the appropriate prepositions in their text. To sum up, the student’s understandings of the use of English prepositions were still low. The suggestions for the next researchers are to work more on the solutions of the sources of the errors made by the students and to analyze the other object besides students’ text, for example on the students’ video project. Keywords: Error, Error Analysis, Preposition, and Descriptive Text