This research aims to (1) Investigate the types of writing strategy employed by the subjects; (2) Find out the differences between the writing strategies used by students with good and poor writing mastery; and (3) Reveal the factors contributing to the use of writing strategy.
    This research was conducted in Muhammadiyah University of Surakarta especially in the English Department of Graduate Program. The subjects of this research are six students who enroll in the English Department of Graduate Program of Muhammadiyah University of Surakarta. The students were categorized into those (three students) with good writing mastery and those (three students) with poor writing mastery by having a writing test. The instruments used for this research were writing test, writing scoring rubric, questionnaire, and interview. Afterwards, the data was analyzed by using flow model by Miles and Huberman (1994).
    Based on the result of analysis, there are some arising research findings that can be sketched: (1) All types of writing strategies were employed by the subjects; (2) Students with good writing mastery employed writing strategies more frequently than those with poor writing mastery; and (3) Factors contributing to the use of writing strategy were identified to be students’ belief, students’ awareness, students’ language proficiency, writing time, writing type, and writing activity environment.
    It can be concluded that employing writing strategies in a high frequency by considering students’ belief, awareness, language proficiency, writing time, writing type, and writing activity environment is strongly essentials as it will help them to achieve a good writing outcome. Therefore it is recommended that: (1) Lecturers need to know their students writing strategy so they can manage their classroom activity in such a way to make it more effective; and (2) Future researchers can use other potential variables besides students writing mastery to conduct a research in this field.

Keywords: Writing, Writing Strategy, Writing Mastery