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Background: To investigate the retinal microcirculation in mild preeclampsia (PE) without obvious retinopathy in high-altitude native Tibetans by optical coherence tomography angiography (OCTA). Methods: This study enrolled 64 mild preeclamptic pregnant women without retinopathy (group PPW), 63 healthy pregnant women (group HPW), and 61 healthy non-pregnant women (group HNPW). All participants were high-altitude native Tibetans who underwent OCTA, retinal thickness (RT), vascular density (VD), perfusion density (PD) and foveal avascular zone (FAZ) parameters were measured in the macula. Differences in these parameters among the groups were compared, and the correlations of these parameters with blood pressure were evaluated. Results: In the entire macula, VD and PD were significantly lower in group PPW than in group HPW and HNPW (p < 0.05). In the subregions, VD was significantly different in fovea, parafovea and perifovea, PD was significantly different in parafovea and perifovea among the three groups (p < 0.05), the further pairwise comparisons showed VD and PD in parafovea and perifovea were lower in group PPW than in group HPW, and VD and PD in perifovea were lower in group PPW than in group HNPW (p < 0.05). RT and FAZ parameters did not differ among the groups (P > 0.05). VD and PD exhibited negative correlations with SBP and DBP (p < 0.05). Conclusion: OCTA can objectively evaluate diminished microcirculation in mild PE without obvious retinopathy among high-altitude native Tibetans, and provide a crucial time window for early screening of PE-induced retinopathy.