The purpose of this study was to find out the politeness strategies used by students of English Department of Mulawarman University academic year 2019/2020 and find out the factors influenced their usage. The design of this was case study within qualitative approach. The subject of this study was students of first, third, fifth, and seventh semester in English Department of Mulawarman University in academic year 2019/2020. The data collected from students’ interaction in Instant Messaging texts to their lecturer and interview sessions were held to support the result of the documents. Moreover, the data analyzed by using content analysis and based on triangulation of data source and investigator to ensure trustworthiness of the data. The result of the study shows that students applied negative politeness, positive politeness, off record and bald on record strategy in their Instant Messaging texts to lectures. Negative politeness strategy was dominated as the way to show respect in communicate to lecturers. Furthermore, relative power and social distance was become the factors influenced students’ usage of politeness strategies. In addition, students’ effort to saving face and the personality of the lecturers also affected it.