Tasked -Based Language Teaching has widely provided learners some opportunities to learn spoken and written language through learning activities in the major of English Language Teaching (ELT). A growing body of research on the effects of task complexity on written productions, the present study explored the impacts of task complexity and strategic planning time on ESL learners' written performance in terms of accuracy. To this end, forty-five undergraduate English Language Learners, both male and female (within the age range of 17-25) have been recruited from Aligarh Muslim University. Two tasks were chosen as instruments for data collection. One is an argumentative essay and the other is a narrative task to measure the accuracy of the participants' written production, under different planning conditions (pre-task planning, withintask planning, and no planning). One-way MANOVA was employed as the statistical means of analysis. The findings revealed a significant effect of task complexity under different planning conditions on Error-free clauses (the percentage of clauses that do not contain any errors) and correct verb forms (the percentage of accurately used verbs in terms of tense, aspect, modality, and subject-verb agreement) regarding accuracy.