Background:BK virus-associated nephropathy (BKVN) is an important cause of chronic allograft dysfunction.The objective of our study was to evaluate the prognosis of BKVN.Methods:We retrospectively reviewed the data of 133 renal transplant recipients with BKVN treated at the First Affiliated Hospital of Sun Yat-Sen University between July 2007 and July 2017.BK viral loads,graft function,and pathologic indexes were compared between initial diagnosis and last follow-up.Results:After a mean follow-up period of 14.4 (range,0.3-109.6) months after diagnosis of BKVN,BK viruria,and BK viremia become negative in 19.5％ and 90.2％ of patients,respectively.The mean estimated glomerular filtration rate (eGFR) at last followup was lower than at diagnosis of BKVN (18.3 ± 9.2 vs.32.8 ± 20.6 mL.min-1.1.73 m-2,t =7.426,P ＜ 0.001).Eight (6.0％) patients developed acute rejection after reducing immunosuppression.At last follow-up,the eGFR was significantly lower in patients with subsequent rejection than those without (21.6 ± 9.8 vs.33.5 ± 20.9 mL·min-1.73 m-2,t=3.034,P =0.011).In 65 repeat biopsies,SV40-T antigen staining remained positive in 40 patients and became negative in the other 20 patients.The eGFR (42.6 ± 14.3 vs.26.5 ± 12.3 mL.min-1 · 1.73 m-2),urine viral loads (median,1.3 × 105 vs.1.4 × 107 copies/mL),and plasma viral load (median,0 vs.0 copies/mL) were all significantly lower in patients with negative SV40-T antigen staining than those with persistent BK involvement (all,P ＜ 0.05).Five (3.8％) recipients lost their graft at diagnosis of BKVN,and 13 (9.8％) lost their graft during the follow-up period.The 1-,3-,and 5-year graft survival rates after diagnosis of BKVN were 99.2％,90.7％,and 85.7％,respectively.Higher pathologic stage correlated with lower allograft survival rate (x2=6.341,P=0.042).Conclusion:Secondary rejection and persistent histologic infection in BKVN lead to poor prognosis.