Tasked Based Language Teaching (TBLT) has widely provided learners with some opportunities to learn spoken and written language through learning activities in the major of English Language Teaching (ELT). In recent years there has been increasing interest in examining differential effects of task complexity and planning time conditions on fluency, accuracy and complexity in English as a second language (ESL) context but, the present study explored the impacts of task complexity and planning time on ESL learners’ written performance in terms offluency. To this end, forty-five undergraduate English Language Learners, both male and female (within the age range of 18-24) 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 fluency of the participants’ written production, under different planning conditions (pre-task planning, within-task 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 in words per minute (the number of words produced by the participants divided by the time they spent on each assignment). Syllables per minute (The number of syllables that the participants produced divided by the minutes they spent on production). Dysfluencies (the number of words they changed or modified in terms of vocabulary or spelling), regarding fluency.