Task-based language teaching (TBLT) is one of the most effective approaches to language teaching. Teachers should provide students with task-based activities which will motivate students to learn. Task-based writing instruction provides educators with effective ways to integrate social and emotional skills with writing skills. The contemporary philosophy of teaching English as a Foreign Language (EFL) encourages collaboration, participation, and engagement. Teachers who advocate collaboration embrace conflicting opinions, strategies, and inquiries constructively while promoting the development of leadership and interpersonal skills. A collaborative educational setting provides tools and techniques that facilitate the interaction of the students with teachers, fellow students, and eventually society. Accordingly, teachers of all disciplines, particularly EFL teachers, must create a collaborative environment that is free of fear to enable the students to develop their skills and abilities. One of the important writing problems faced by second-language (L2) learners is the lack of self-efficacy and epistemic beliefs. The widespread use of task-based writing in EFL classes, as well as the growing interest in the role of self-efficacy and epistemic beliefs, beg the question of whether or not such an approach to writing instruction contributes to the learners' self-efficacy, epistemic belief, and eventually their sense of identity and confidence. This study aimed to address this concern. To the best knowledge of the researcher, few, if any, studies have been conducted on the effect of task-based writing instruction on EFL learners' self-efficacy and epistemic beliefs. Accordingly, this study aimed to address this gap by investigating the mentioned effect on the Iranian Intermediate EFL learners.