Background: The systemic inflammatory index (SII) is a new inflammatory marker that has been the subject of various studies in diseases with chronic inflammation. Diabetic nephropathy is a disease associated with chronic inflammation. We aimed to evaluate the relationship between SII and diabetic nephropathy. Methods: Patients with diabetes who applied to our outpatient clinic were included in the study. Diabetic patients were divided into two groups: those with diabetic nephropathy and those without. In addition, healthy individuals who applied to our clinic for general check-ups during these dates were included as the control group. The SII values and other characteristics of the three study groups were compared. Results: The median SII value for those with DKI was 584 (178–4819); for those without DKI, it was 282 (64–618); and for the control group, it was 236 (77.5–617) (p< 0.001). SII was significantly and positively correlated with BMI, weight, blood glucose, HbA1c, CRP, and creatinine, and negatively correlated with the glomerular filtration rate (GFR) value. SII values higher than 336 have 75% sensitivity and 70% specificity in detecting DKI. Conclusion: The SII value can predict diabetic kidney injury in diabetics, and it can be used as an adjunctive diagnostic tool.