Task-evoked pupil response (TEPR) has been extensively studied and well proven to be sensitive to mental workload changes. We aimed to explore how TEPR reflects mental workload changes in a surgical environment. We conducted a simulated surgical task that has 3 different subtasks with different levels of motor precision and different mental workload requirements. We found a significant effect among these different subtask groups by measuring pupil diameter change rate. This finding may improve patient safety in a real operating room by non-intrusively monitoring the surgeon's mental workload while performing a surgery using an eye-tracking system.