Chronic allograft injury (CAI) is common after kidney transplantation and the leading cause of allograft loss in kidney transplant recipients (KTRs). The aim of this study was to investigate urinary biomarkers associated with CAI and rapid renal function decline in KTRs. Thirty KTRs whose estimated GFR were less than 60 mL/min/1.73m2 (CAI group) and 20 KTRs with normal allograft function (control group) were included in this study. To identify potential urinary biomarkers, we performed SDS-PAGE followed by liquid chromatography-mass spectrometry (LC-MS/MS). Several urinary proteins including beta-2-microglobulin (B2MG) were validated by ELISA. Rapid renal function decline was defined as estimated GFR decline of >3 mL/min/1.73m2/year or initiation of dialysis for 3 years after baseline sampling.  Among protein profiles identified by proteomics, urinary B2MG levels were different between CAI group and control group (9882.0 vs. 1165.7, P<0.001). Urinary B2MG levels measured by ELISA were also higher in CAI group (1686.4±2997.8 vs. 28.1±27.5 ng/mL, P=0.005). Urinary B2MG/creatinine levels had high association with CAI group compared to control group (AUROC 0.770 [0.641-0.899], P<0.001). Among 50 KTRs, 19 patients (38%) were classified as rapid renal function decline group. Urinary B2MG levels were higher in rapid renal function decline group than stable renal function group (2253.5±3615.4 vs. 269.0±631.6 ng/mL, P=0.029). Higher urinary B2MG levels (>2347 ng/mL) were associated with significantly lower graft survival compared to lower urinary B2MG levels (<2347 ng/mL) (log rank test: P=0.006). These results suggest that urinary B2MG levels might be a potential biomarker for detection of CAI and could be used as predictor for rapid renal function decline in KTRs.