<![CDATA[Scientific writing requires the use of language in accordance with the rules of the Indonesian language, especially in compiling sentence structures and applying effective sentence principles. However, various syntactic errors are still common in undergraduate student theses, which can reduce the clarity of the ideas presented. This study aims to describe the forms of sentence structure errors and ineffective sentence use found in the undergraduate thesis of students of the Department of Indonesian Language and Literature Education, Nurul Huda University which will be completed in 2024. This research uses a qualitative descriptive approach, with data obtained from three undergraduate theses, especially from Chapters I and IV. Data is collected through observation, reading, and recording techniques and is analyzed by identifying, classifying, and describing each type of error. These findings reveal that the most common errors include incorrect Subject-Predicate-Object-Complementary (SPOC) sentence structures, words, ambiguous sentences, and incomplete sentences. Among the three theses analyzed, words were identified as the most dominant type of error, followed by inappropriate sentence structures, ambiguous sentences, and sentences that lacked complete syntactic elements. These findings suggest that students' understanding of syntactic rules and effective sentence construction principles still needs to be improved. Therefore, this research is expected to be a source of evaluation of academic writing teaching as well as help students in improving their ability to use Indonesian accurately, correctly, and effectively.]]>
