Aims. This study aimed to compare the accuracy of the choroidal vascularity index (CVI) and diabetic retinopathy (DR) in the diagnosis of diabetic nephropathy (DN). Methods. We performed a cross-sectional study of 117 patients with proteinuria and diabetes mellitus (DM) in which 45 patients were diagnosed with DN by renal pathology. Demographic information, clinical features, and laboratory data were collected. A total of 234 eyes underwent evaluation of DR and the CVI using enhanced depth imaging-optical coherence tomography scans. We analyzed the association between the CVI and DN and compared the CVI and DR for diagnosing DN using area under receiver operating characteristic curves (AUROCs). Results. The severe nonproliferative DR and proliferative DR groups showed a lower CVI than the no DR and mild/moderate nonproliferative DR groups (P < 0.01 or P < 0.001). There was a significantly lower CVI in patients with DN stage III (63.01% +/- 1.47%) compared with those in DN stages IIa (62.1% +/- 1.41%, P < 0.001) and IIb (59.85% +/- 1.98%, P < 0.01). The sensitivity and specificity of the CVI for diagnosing DN were 84% (71%-94%) and 95% (88%-99%), respectively, which were preferable to those of DR. The AUROCs for the CVI and DR for diagnosing DN were 0.932 and 0.831, respectively. The CVI outperformed DR for diagnosing DN (P < 0.05). The cutoff value of the CVI was 63.13%. Conclusion. The CVI might be a reliable noninvasive technique for predicting the pathological stage of DN and is superior to DR in diagnosing DN.