Learner individual differences can play differential roles in learners’ performance on different task types of different complexity levels. This study investigates the differential role of domain-specific anxiety in second language (L2) learners’ performances on narrative and argumentative writing tasks. For this purpose, a group of 102 upper-intermediate L2 learners in Iran were asked to perform either a narrative or an argumentative writing task. The study also involved the measurement of learners’ L2 writing anxiety using the Second Language Writing Anxiety Inventory (SLWAI) that represents somatic anxiety (negative feelings such as tension), cognitive anxiety (negative expectations, preoccupation with performance) and avoidance behavior (avoidance in writing). Moreover, the quality of learners’ writings was assessed by eliciting three measures of task performance, i.e. Complexity (clauses per T-unit and dependent clauses percentage), Accuracy (error-free clauses and T-units percentage) and Fluency (average number of words, T-units and clauses per text). Regarding the narrative task, negative relationships were found between cognitive anxiety and both accuracy measures; further, a significant negative correlation was found between somatic anxiety and an accuracy measure of narrations. On the contrary, the effect of writing anxiety on argumentative task performance was more extensive: negative correlations were observed between cognitive anxiety and all three measures of fluency, one complexity measure and one accuracy measure; avoidance behavior was also negatively associated with two fluency measures and one complexity measure. The implications of the study are discussed.