Providing feedback to students on their writing represents perhaps the most important task. It discussed the importance of supervisors' written feedback on Jordanian master's students. It discusses the feedbacks in terms of content, and methods. The purpose of this paper was to discover the types of errors that Jordanian master's students who are majoring in English language at Yarmouk University made when they write their master's thesis. The researcher analyzed 9 Jordanian master theses based on their supervisors' comments. The researcher has discovered three main themes such as coherence problems, mechanism problems of writing, and problems with organizing the thesis.