Objectives: This study compared the clinical and pathologic presentation and renal prognosis in patients with pure diabetic nephropathy (DN) and those with DN combined with other renal pathology (mixed DN). Methods: This is a retrospective study using a kidney biopsy registry data from eight university hospitals in South Korea. Among 215 patients with type 2 diabetes who had undergone renal biopsy, 75 patients were diagnosed as DN, and were further categorized into pure DN and mixed DN according to renal histology. Clinical data, renal histological findings, and renal prognosis were compared between pure DN and mixed DN. Results: There were 46 patients (61.3%) with pure DN, and 29 patients (38.7%) with mixed DN. There was no significant difference in demographic findings, blood pressure, proteinuria, estimate glomerular filtration rate (eGFR), presence of diabetic retinopathy or hematuria, or anti-diabetic drugs between the two groups. The degree of glomerulosclerosis, mesangial expansion, or interstitial fibrosis did not differ between the two groups. More neutrophil infiltration in tubulointerstitium (P = 0.017) and acute tubular necrosis (P < 0.001) were found in mixed DN patients compared with pure DN patients. The eGFR decline rate was significantly higher in pure DN group (-1.67±2.65 mL/min/ month) compared with mixed DN group (-0.19±1.59 mL/min/ month, P = 0.031). More patients in pure DN group (23.9%, n = 11) started renal replacement therapy than those in mixed DN group (6.9%, n = 2) during follow-up (P = 0.001). Conclusions: Although there was no significant difference in clinical characteristics between the two groups, renal prognosis was better in mixed DN patients than pure DN patients. Therefore, a more accurate pathologic diagnosis through kidney biopsy may improve the clinical outcomes of patients with DN.