To assess incidence and risk factors of postoperative progressive nasal inner nuclear layer (INL) thickening after epiretinal membrane (ERM) surgery. Progressive nasal INL thickening was defined as 1.5-fold increase in thickness of nasal INL after ERM surgery compared to preoperative examination. Kaplan-Meier survival analysis was done to compare the cumulative risk ratio between groups stratified by presence of progressive nasal INL thickening. Logistic regression was performed to identify possible risk factors. Progressive nasal INL thickening occurred in 13.0% of ERM removal patients. Patients without progressive nasal INL thickening showed better visual acuity recovery compared to patients with nasal INL thickening (p = 0.029). Presence of cystoid space in inner retinal layer before surgery (odds ratio OR = 0.143, 95% confidence interval CI 0.028-0.736; p = 0.020), older age (OR = 0.896, 95% CI 0.817-0.982, p = 0.020), and thicker preoperative central macular thickness (OR = 0.994, 95% CI 0.988-1.000, p = 0.039) were correlated inversely with thickening of nasal INL. Correlation between nasal INL thickness and postoperative visual outcome was significant. Absence of cystoid space before ERM surgery, younger age, and thinner central macular thickness were risk factors for progressive postoperative nasal INL thickening. Progressive nasal INL thickening may serve as a new biomarker for worsened visual symptom after ERM surgery.