Background: Given that unilateral branch retinal vein occlusion (BRVO) and glaucoma share common systemic vascular risk factors, the fellow eyes of patients with BRVO may be at increased risk of glaucoma. Objectives: To analyze the radial peripapillary capillary density (RPCD) in eyes with unilateral BRVO and their unaffected fellow eyes using optical coherence tomography angiography (OCTA). Design: Cross-sectional, prospective study. Methods: The study included 120 eyes of 80 patients: 40 affected eyes of BRVO, 40 fellow eyes of BRVO, and 40 control eyes. The RPCD, retinal nerve fiber layer thickness (RNFLT) were analyzed using OCTA. Results: RPCDs in the whole image, peripapillary region, all the hemispheres, and quadrants were statistically lower in the affected eyes than in both the fellow and control eyes (p < 0.05 for all). RPCD values in the whole image and the peripapillary region were significantly lower in the fellow eyes than in the control eyes (p = 0.013, and p = 0.021, respectively). RNFLTs in the peripapillary region, inferior hemisphere and inferior quadrant were significantly lower in the affected eyes than in the control eyes (p < 0.05 for all). No significant differences were detected between the fellow eyes and the control eyes in term of RNFLT values in any regions (p > 0.05 for all). Conclusion: Lower RPCD values despite similar RNFLT values were observed in the fellow eyes of patients with unilateral BRVO compared with healthy controls. These results may indicate the shared vascular mechanisms and risk factors that account for the development of BRVO and glaucoma. Keywords: branch retinal vein occlusion; glaucoma; optical coherence tomography angiography; radial peripapillary capillary density; retinal nerve fiber layer thickness.