Purpose: To investigate the natural history of idiopathic epiretinal membrane (ERM) in eyes with good visual function using optical coherence tomography (OCT). Methods: Sixty-two eyes of 58 patients with idiopathic ERM, visual acuity of 20/40 or better, and no significant metamorphopsia were included. The best corrected visual acuity (BCVA), central macular thickness (CMT), membrane configuration, and ellipsoid zone signal data over 24 months were retrospectively analyzed. Based on OCT findings, ERM configurations were categorized as global attachment (GA), partial attachment (PA), pseudohole, and vitreomacular traction (VMT). Results: The mean BCVA and CMT did not change significantly between baseline and 24 months. GA, PA, pseudohole, and VMT types were observed in 33, 19, 9, and 1 eye at baseline, and in 20, 22, 10, and 1 eye at 24 months, respectively. A membrane configuration change was noted in 24 eyes (38.7%) during follow-up, and the distribution shifted from GA to the other types (p < 0.001). Six eyes had visual loss due to membrane progression, and 4 eyes had spontaneous membrane separation. Of the 10 eyes with progression or separation, 6 were of the PA type. Conclusions: Although the BCVA remains stable over 2 years in most idiopathic ERM eyes with good visual function at baseline, the membrane configuration may change, affecting visual acuity. The GA type would be an early stage, and the PA type is prone to changes in visual acuity.