Academic writing is a major concern for many university students. Despite extensive literature on students’ academic writing, little attention has been focused on students’ writing experience and practice in higher education. To fill this gap, the present study compared actual and perceived academic writing competence of postgraduate students who were enrolled in English for Academic Purposes (EAP, hereafter) courses. First, measures of actual and perceived academic writing competence were developed and validated in Phase 1, using a separate sample of EAP postgraduate students (n = 391) in Ilam province, Iran. Phase 2 examined postgraduate students’ academic writing competence perceptions and the ways through which their perceptions might have differed from their actual academic performance. Then the developed measures of actual and perceived academic writing competence, which exhibited acceptable reliability and good model-data fit, were distributed among a sample of 210 EAP postgraduate students from nine different academic fields. The results of data analysis revealed significant differences in perceptions and actual academic practices of students across different academic fields of study.