The impetus of the present study was to investigate the impact of self-efficacy and proficiency on EFL learners‘ written task performance regarding concept load, fluency, complexity and accuracy. One hundred and forty four low-proficiency and high-proficiency learners of English as a foreign language, between ages 18-25, were chosen. Each participant was requested to execute three tasks: a narrative task, a personal task, and decision-making task and fill out the self-efficacy questionnaire. The participants‘ performances were then analyzed utilizing the Pearson correlation. The results demonstrated that there was a significant relationship between self-efficacy and narrative and personal tasks in terms of concept load but not in terms of fluency, complexity, and accuracy in high proficiency participants. Also, there was no relationship between self-efficacy and decision-making tasks in terms of concept load, fluency, complexity, and accuracy in both low and high proficiency participants.