Purpose: To explore the clinical features and significance of “notch” in reactivation of retinopathy of prematurity (ROP) post–intravitreal ranibizumab (IVR) monotherapy. Methods: Ninety-six infants (173 eyes) with Type 1 or aggressive ROP (A-ROP) post-IVR monotherapy were retrospectively analyzed; 51 eyes were notch (+) and 122 eyes were notch (−). General demographics and clinical outcomes were compared by notch status for Type 1 and A-ROP. Results: The notch primarily appeared in Stage 2 ROP (84.4% and 78.9%) at the junction of Zones I and II (68.8% and 63.2%) on the temporal side in Type 1 ROP and A-ROP. Notch was present in the Type 1 ROP group before first IVR but posttreatment in the A-ROP group. A significantly higher reactivation rate, longer follow-up duration, and postmenstrual age at the last follow-up were seen in the notch (+) versus the notch (−) group. In the notch (+) ROP group, the mean gestational age (28.34 ± 0.93 vs. 29.94 ± 1.48 weeks) was significantly lower in reactivated versus regressed eyes. Conclusion: Notches appeared at different times but similar locations in Type 1 ROP and A-ROP. The reactivation rate after IVR was increased in ROP with notches. Notch may be a useful biomarker for reactivation after IVR in ROP.