Abstract-One of the hotly debated areas of research in second language acquisition since 1990s has been pertained to the role of consciousness in learning second or foreign language. A review of the studies conducted on different aspects of consciousness in second language acquisition revealed there is a gap in the literature on the effect of focus on from instruction on L2 learners' oral or written task performance across different proficiency levels. Therefore, the present study set out to fill the existing gap in the literature and investigate the effects of form-focused instruction on L2 learners' written task performance in terms of accuracy across two different proficiency levels (intermediate and advanced). To this end, sixty learners of English studying English in an institute were randomly chosen as the participants of the study. They were randomly divided into two groups of high and low proficiency levels. The two groups were also divided into two subgroups of with and without F-O-F. All groups were taught for 15 sessions. However, one subgroup of each group received form-focused instruction while the other two subgroups did not receive the treatment. A pictorial narrative task was employed as the post-test instrument to collect the written data. The collected written data were quantified and measured according to measures introduced by Ellis (2003). The findings of the study revealed that form-focused instruction had a significant effect on the accuracy of high proficient learners. The study carries some implications for second language acquisition researchers, language teachers, and syllabus and task designers.Index Terms-focus on form, focus on forms, form-focused instruction, proficiency level, accuracy