Objective: To investigate the value of neutrophil gelatinase-associated lipocalin (NGAL) and reticulocyte percentage (Ret%) in differentiating acute kidney injury (AKI) from chronic kidney disease (CKD). Methods: The study included 437 patients with nephropathy from the Department of Nephrology of the First Affiliated Hospital of Nanjing Medical University. The subjects were divided into AKI group (n = 140) and CKD group (n = 297). To control potential selection bias, propensity matching analysis of 19 variables was used to compare the urine/serum NGAL (u/sNGAL) and Ret% between the two groups. According to the stratification of renal function, the differentiation ability of u/sNGAL and Ret% in AKI and CKD was compared. Results: The product of u/sNGAL and Ret% (u/sNGAL ×Ret%) in AKI group was significantly higher than that in CKD group (1.74 (0.79- 4.16) vs 0.28 (0.15- 0.55), P < 0.001). Propensiy-matched analysis included 46 patients in each group. In matched patients with AKI and CKD, Ret%, u/s NGAL, and u/s NGAL×Ret% were significantly increased in the AKI group (1.75 (1.26- 2.53) vs 1.37 (1.16- 1.83)). 0.64 (0.33- 1.52) vs 0.31 (0.13- 0.76) and 1.27 (0.59- 3.31) vs 0.46 (0.25- 1.53)) . In all patients (n = 437), the receiver operating characteristic (ROC) analysis showed that Ret%, u/sNGAL and u/sNGAL×Ret% could distinguish AKI from CKD (the area under the curve was 0.701, 0.847 and 0.868, respectively). After stratified by renal function, subgroup analysis showed that there were significant differences in u/sNGAL×Ret% between AKI group and CKD group (P < 0.01). In the subgroup analysis of patients with eGFR > 60mL/min/1.73m2, both u/sNGAL×Ret% and Ret% were able to differentiate AKI from CKD. However, in the subgroup analysis of patients with eGFR < 60mL/min/1.73m2, u/sNGAL×Ret% demonstrated superior performance in distinguishing AKI from CKD compared to Ret% (P < 0.05). Conclusion: u/sNGAL×Ret% can be used as an indicator for the differential diagnosis of AKI and CKD patients in the Department of Nephrology.