AIM: To quantify early changes of macular capillary parameters in type 2 diabetic patients using optical coherence tomography angiography(OCTA).METHODS: Retrospective case study. A total of 49 healthy subjects, 52 diabetic patients without retinopathy(noDR)patients, and 43 mild nonproliferative diabetic retinopathy(mNPDR)patients were recruited. Capillary perfusion density, vessel length density(VLD), and average vessel diameter(AVD)were calculated from macular OCTA images(3 mm×3 mm)of the superficial capillary plexus after segmenting large vessels and the deep capillary plexus. Parameters were compared among control subjects, noDR, and mNPDR patients. The area under the receiver operating characteristic curve estimated the abilities of these parameters to detect early changes of retinal microvascular networks.RESULTS: Significant differences were found in the VLD and AVD among the three groups(P<0.001). Compared with the control group, the noDR group had significantly higher AVD(P<0.05). VLD of both layers in patients of mNPDR group was significant decreased compared with that of noDR group(all P<0.01). Deep AVD had a higher area under the curve(AUC)of 0.796 than other parameters to discriminate the noDR group from the healthy group. Deep AVD had the highest AUC of 0.920, followed by that of the deep VLD(AUC=0.899)to discriminate the mNPDR group from the healthy group.CONCLUSIONS: NoDR patients had wider AVD than healthy individuals and longer VLD than mNPDR patients in both layers. When compared with healthy individuals, deep AVD had a stronger ability than other parameters to detect early retinal capillary impairments in noDR patients.