Writing knowledge is the key requirement that students have to possess to compose a good argumentative essay. However, their unawareness affects negatively their writing ability to produce good quality essays. This article examines second year Libyan (EFL) university students' awareness about the types of writing knowledge used in composing an argumentative essay and how it influences their essay quality. A methodological triangulation was employed in this study. Tools for collecting data were focus-group interviews, writing tasks and observations. Thirteen undergraduate female students at Al Asmarya Islamic University, Libya participated in the study. Data was triangulated and analyzed using thematic and content analysis. The findings show that the participants had different levels of awareness about types of writing knowledge while composing an argumentative essay. Most students had novice awareness of writing knowledge. The results also revealed that students' novice awareness forced them to face many problems in writing an argumentative essay which in turn led them to produce very poor-quality essays.