Eye-Tracking technology has been applied to surgical skill improvement and can observe differences in gaze data between the experienced and novice surgeon. Some eye trackers can even detect pupil diameter. We hypothesized that differences in technical proficiency among surgeons affect the extent of changes in pupil diameter, because the higher mental workload a laparoscopic task requires, the larger the person's pupil diameter dilates. In this study, we recorded the pupil diameters of pediatric surgeons while they performed a suturing task in a dry box environment. The more proficient surgeons exhibited a smaller distribution in pupil diameter than did the less proficient surgeons. Our data indicate that an individual's suturing proficiency is closely related to the degree of dispersion of pupil diameter.