Objective To observe the pathological changes of branch retinal artery occlusion (BRAO) by optical coherence tomography (OCT). Methods Twenty-six eyes of 26 patients with BRAO diagnosed in our Center from December 2002 to June 2005 were examined by OCT. The intervals of disease onsets and OCT examinations in all patients were within 2 weeks. The OCT scan modes were horizontal or vertical lines, and the locations of OCT scanning were macular area and the posterior pole of retina. The retinal thicknesses of macular foveola were measured and the macular thicknesses in different obstructive locations were compared using ANOVA analysis. The correlations of visual acuity and retinal thickness were analyzed by Pearson correlation analysis. Results Among the 26 eyes with BRAO, 9 eyes with temporosuperior artery occlusion, 8 eyes with temporoinferior artery occlusion, 7 eyes with arteriole occlusion and 2 eyes with retinal ciliary artery occlusion were observed. The pathological characteristics of OCT images of BRAO were increased retinal thickness and reflectivity in the obstructive locations, and widened dark area of photoreceptors (edema), while there was no obvious foveal edema were observed. The retinal images in other locations were normal. The average macular foveal thickness in the groups of temporosuperior artery occlusion, temporoinferior artery occlusion and retina arteriole occlusion were (161.11plusmn;17.66) mu;m, (148.38plusmn;18.48) mu;m and (136.29plusmn;14.94) mu;m, respectively (F=4.137,P=0.031,Pgt;0.01). There was no correlation of visual acuity with retinal thickness in 24 eyes (r＝0.285，P＝0.176，Pgt;0.01). Conclusion OCT could display the pathological changes of retinal tissue of BRAO in vivo. The increases of macular foveal thicknesses in BRAO eyes are not so obvious, and no correlations could be seen between visual acuity and macular foveal thickness. OCT is indicated on the old patients and the patients with systemic diseases for whom FFA is contraindicated. The unique characteristics of pathological changes of BRAO indicated by OCT images supply the objective signs for the instant clinical diagnosis. (Chin J Ocul Fundus Dis, 2007, 23: 173-176)