In the field of teaching EFL students the process of writing an essay, this study was conducted to investigate the influence of diary writing on the students’ writing and language abilities. 52 student participants enrolled in two Advanced Writing classes wrote a daily diary for 14 weeks. During this period, they were given essay writing lessons, and were asked to write four essays throughout the semester. At the end of the semester, the students were given an open-ended questionnaire requesting information about the students’ method of diary writing and its benefits. The analysis of the data obtained showed that the students’ language abilities significantly improved especially the grammar and vocabulary. The students also reported their satisfaction in the free-writing method which allowed them to learn more on self-expression and organization of ideas. The researchers believe that a skilful writing teacher would be able to provide maximum benefit from this experience. This study is believed to be extremely beneficial to language teachers, and more specifically, EFL writing teachers.