BACKGROUND: A biomarker, by which we can predict alterations of renal function in normoalbuminuric diabetic patients, is not available. Here, we report that endogenous anti-fibrotic peptide N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) represents a potential biomarker to predict alterations in eGFR in normoalbuminuric diabetic patients. METHODS: We analyzed 21 normoalbuminuric diabetic patients with eGFR ≥ 30 ml/min/1.73 m2 and measured AcSDKP levels in first morning void urine. We divided patients into two groups based on the median values: low or high urinary AcSDKP groups (uAcSDKP/Crlow or uAcSDKP/Crhigh). At baseline, no significant differences in sex, age, HbA1c, BMI, serum creatinine levels, etc., were observed between the two groups. RESULTS: During ~ 4 years, the alteration in eGFR [ΔeGFRop (ΔeGFR observational periods)] was significantly stable in uAcSDKP/Crhigh group compared with uAcSDKP/Crlow group over time (P = 0.003, χ2 = 8.58). We also evaluated urine kidney injury molecule-1 (uKim-1) levels and found that ΔeGFRop was also stable in low uKim-1 group compared with high uKim-1 group over time (P = 0.004, χ2 = 8.38). Patients who fulfilled the criteria for both uAcSDKP/Crhigh and uKim-1low exhibited stable ΔeGFRop (P < 0.001, χ2 = 30.4) when compared to the remaining patients. Plasma AcSDKP (P = 0.015, χ2 = 5.94) and urine β2-microglobulin (P = 0.038, χ2 = 4.31) also display weak but significant predictor of ΔeGFRop as well. CONCLUSION: AcSDKP represents a potentially useful biomarker to predict alterations in the renal function of patients with diabetes presenting normoalbuminuria.