To evaluate the effects of intravitreal ranibizumab injection (IVR) on metamorphopsia in patients with branch retinal vein occlusion (BRVO) and to assess the relationship between retinal microstructure and metamorphopsia. Subjects were 39 eyes of 39 patients with branch retinal vein occlusion. The severity of metamorphopsia was quantified using the M-CHARTS before and 1, 2, 3, 4, 5, and 6 months after treatment. Based on optical coherence tomography (OCT) images, we assessed central retinal thickness (CRT) and status of the external limiting membrane (ELM) and ellipsoid zone (EZ). The association between retinal microstructure and metamorphopsia was analyzed in 24 eyes with treatment-naïve branch retinal vein occlusion. Intravitreal ranibizumab injection treatment significantly improved best-corrected visual acuity (BCVA) and central retinal thickness (P < 0.0001, P < 0.0001, respectively), but metamorphopsia did not improve by treatment. Posttreatment metamorphopsia scores showed a significant correlation with duration of symptoms (P < 0.05) and pretreatment metamorphopsia scores (P < 0.01). Posttreatment metamorphopsia score was significantly worse in patients with disruption of external limiting membrane (P < 0.05). In patients with branch retinal vein occlusion, intravitreal ranibizumab injection treatment significantly improved best-corrected visual acuity and central retinal thickness, but not metamorphopsia. The severity of posttreatment metamorphopsia was significantly associated with duration of symptoms, degree of pretreatment metamorphopsia, and posttreatment integrity of external limiting membrane.