Task-based language Teaching (TBLT) has been formed as an approach wherein learners are allowed to communicate language use through tasks due to the limitations of the traditional PPP (Presentation, Practice, and Performance) approach. Among different kinds of tasks, according to Ellis (2008), convergent/divergent tasks can be mentioned which have been originated from concepts of knowledge formation. At a broader level, tasks are divided into input-based tasks and output-based tasks. This study aimed at investigating the effect of output-based and input-based divergent and convergent tasks on learning English idioms among Iranian EFL intermediate-level learners. In so doing, this study used a quantitative quasi-experimental pre-test post-test control group design. The participants of the study consisted of 75 male intermediate EFL learners studying English at a private language institute in Zahedan, Iran, who were selected through convenience sampling. To collect the data, Oxford Placement Test (OPT) and two researcher-made idiom tests were used. To analyze the data, descriptive statistics and inferential statistics were run. The results showed that output-based and input-based divergent and convergent tasks had a significant effect on learning English idioms among Iranian EFL intermediate-level learners. The findings have some implications for EFL teachers, learners, and curriculum planners.