AIM: To measure the retinal oxygen saturation in healthy subjects and early branch retinal vein occlusion (BRVO) in Chinese population. METHODS: The retinal vessel oxygen saturation of the healthy subjects and BRVO patients were measured by a noninvasive retinal oximeter (Oxymap ehf., Reykjavik, Iceland). RESULTS: The study included 22 patients with unilateral BRVO (mean age: 55.1 +/- 8.8y) in the study group and 91 healthy participants (mean age: 37.5 +/- 14.0y) in the control group. In the healthy individuals, mean arterial and venous oxygen saturation were significantly (P<0.001) higher in the superior nasal quadrant (98.5%+/- 10.1% and 57.3%+/- 8.7%, respectively) than in the inferior nasal quadrant (94.2%+/- 9.0% and 54.1%+/- 9.6%, respectively), followed by the superior temporal quadrant (89.1%+/- 10.1% and 51.9%+/- 8.9%, respectively) and the inferior temporal quadrant (86.4%+/- 9.4% and 46.6%+/- 9.6%, respectively). In patients with ischemic BRVO, arterial oxymetric values were significantly higher and venous measurements significantly lower for the affected vessel (107.5%+/- 9.7% and 46.4%+/- 14.2%, respectively) than the unaffected vessel in the same eye (99.2%+/- 12.2% and 55.5%+/- 7.9%, respectively) and as compared to the vessel in the unaffected fellow eye (93.1%+/- 6.9% and 55.7%+/- 6.8%) (Rho=0.005 and Rho=0.02, respectively). In the patients with non-ischemic BRVO, mean venous oxygen saturation was lower in the affected vein (39.8%+/- 12.2%) than in the unaffected vessels of the same eye (50.8%+/- 10.5%) and in the fellow eye (58.21%+/- 5.7%) (Rho=0.03). Mean arterial oxygen saturation did not differ significantly (Rho=0.42) between all three groups. CONCLUSION: In patients with BRVO, the venous oxygen saturation in the affected vessels is decreased potentially due to decreased blood velocity and flow. Interestingly, the arterial oxygen saturation in eyes with ischemic BRVO is increased in the affected arteries.