English as a Foreign Language (EFL) learners may not appreciate writing and even perform poorly in writing tasks partly due to what feelings they harbor toward such tasks. This study explored the relative effects of three degrees of writing task complexity based on resource directing dimensions of complexity on EFL learners' task motivation. Participants were 64 intermediate EFL learners at a language school in Baneh, Kurdistan, Iran, and were randomly assigned to one of the three groups: low complexity group, medium complexity group, and high complexity group. After completing the tasks, they filled in a task motivation questionnaire. The results showed that perceived relevance as a dimension of task motivation was higher in medium complexity group. With respect to emotional state as another dimension of task motivation, medium complexity task motivated participants more than low and high complexity tasks, because the participants showed a positive emotional state after doing it. Based on the findings and regarding intermediate EFL learners, it is recommended that writing tasks with a medium degree of complexity should be incorporated into task-based syllabuses by EFL teachers because of learners' task motivation toward these tasks.