The study aims at analyzing errors made by Sudan University of Science and Technology students' at faculty of Sciences-Chemistry Department in employing passive voice in writing lab reports. The study focuses precisely on identifying the types of errors occurred in using passive voice and the reasons behind these errors. Descriptive qualitative method is adopted and applied to obtain and process the gathered data. To run this study and to collect reliable data, thirty chemical students are chosen randomly as the subject of the study. Samples of the students' lab reports are collected and analyzed. The collected data is analyzed according to the Dulay et al. (1982) Surface Strategy Taxonomy model. Teachers' questionnaire is also used to find out the sources of the students' errors from the teachers' point of view. The findings of the study reveals that the majority of the students' errors are categorized as omission and misinformation whereas additions and misordering errors are fewer and unconsidered. According to the teachers, these errors are attributed to the interference of the mother tongue, lack of knowledge and carelessness of the students.