%K Errors analysis, intralingual errors, writing, English %X Nowadays, students are expected to be able to write a research report to fulfill their final assignments. Hence, recognizing errors in order to improve students' ability in writing is considered important. Common causes of errors can be due to the influence of the first language or mother tongue (interlingual errors) or lack of mastering the target language (intralingual errors). The results of previous research show that the biggest cause of errors deals with the lack of students’ mastering in the target language. Therefore, this research focuses on analyzing intralingual errors made by the undergraduate students the fourth semester at Ahmad Dahlan University. This research was conducted qualitatively where the researcher acted as the main instrument. Writing tests and interviews were carried out to obtain the data from the undergraduate students from Ahmad Dahlan University, and their writing texts were being the subject of this research. The objects of the research are words, phrases, and sentences that indicate intralingual errors. The steps of data analysis begin with (1) collecting errors data made by students, (2) identifying errors (3) describing errors, (4) explaining errors (5) evaluating errors. These data were then analyzed by using James’ intralingual errors theory. The results of this research showed that the highest percentage of intralingual errors was found in overgeneralization (41.00%), followed by overlooking co-occurrence restrictions (39.15%), exploiting redundancy (6.63%), misanalysis and incomplete rule applications which had similar result (4.81%), and the lowest percentage was found in false analogy and hypercorrection (1.80%). From the result of interviews with the students, it can be concluded that the internal factors are the main cause of students in making errors. In addition, it seems that the students’ motivation and learning habits affect their mastery of grammar and vocabulary in the target language. In short, this research is expected to be able to contribute to teachers in finding innovations and strategies in learning to write in order to minimize errors made by students. Expectantly, the students are able to write properly in English as well as pay more attention to their strategies and motivation in learning English. %A Yuli Nurmala Sari %A Margana Margana %L UNY67849 %I Program Pascasarjana %D 2019 %T The Intralingual Errors on Writing Performed by English Department Students at the Fourth Semester of Ahmad Dahlan University.