Clinical management and therapeutic intervention from the earlier stage of diabetic nephropathy (DN) is of major importance to prevent the progression of DN to end stage renal disease. At present, the measurement of albuminuria is used as a standardized non-invasive test for the diagnosis of early DN. Diabetic kidney disease, however, is not detected by this test in some cases. Hence, efforts have been made to find better diagnostic biomarkers of DN. These investigations have identified several proteins that can be used as diagnostic biomarkers of DN, including urinary immunoglobulin G, transferrin, ceruloplasmin and serum cystatin-C. Further, recent proteomics approaches have isolated potential biomarkers of DN. This review summarizes the diagnostic biomarkers developed over the last decade, and comments on their impacts in the diagnosis and management of this disease.