Purpose: To compare 0.5 mg and 0.625 mg of bevacizumab for treating aggressive posterior retinopathy of prematurity (AP-ROP). Methods: The medical records of patients with AP-ROP who were administered intravitreal bevacizumab (IVB) as a primary treatment at a university clinic were evaluated retrospectively. Five eyes of three patients (Group 1) who received 0.625 mg/0.025 ml IVB and 10 eyes of another five patients (Group 2) who received 0.5 mg/0.02 ml IVB were evaluated. Laser photocoagulation was used as additional treatment after relapses. Anatomic results and complications were evaluated in both groups. Results: We evaluated 15 eyes of eight patients (four girls and four boys) with a flat demarcation line at posterior zone 2 and plus disease or stage-3 disease in this study. The mean gestational age of the three babies in Group 1 was 26 +/- 1 weeks and the mean birth weight was 835.33 +/- 48.01 g. The corresponding values were 25.2 +/- 1.6 weeks and 724 +/- 139.03 g, respectively, for the five babies in Group 2. Retinal vascularization was completed at a mean postmenstrual duration of 53.6 +/- 1.5 weeks without additional treatment in the five eyes in Group 1. Laser photocoagulation for relapse was administered to five of the 10 eyes in Group 2. Retinal vascularization was completed at a mean postmenstrual duration of 47.6 +/- 1.5 weeks in the remaining five eyes. None of the patients developed complications such as cataract, glaucoma, retinal tear, retinal or vitreous hemorrhage, or retinal detachment. Conclusion: Although lower IVB doses in the treatment of AP-ROP are expected to be safer in terms of local and systemic side effects in premature infants, these patients may require additional treatment with IVB or laser photocoagulation.