Objective:To explore the clinical value of peripheral blood lymphocyte subsets in the differential diagnosis of BK virus nephropathy (BKVN) in renal transplantation recipients.Methods:From 2014 to 2018, a total of 172 renal transplant recipients were recruited. Their peripheral blood lymphocyte subsets were detected. According to the pathological puncture results of transplanted kidney, they were divided into acute rejection group (AR, n=68), BKVN group ( n=73) and stable graft function group (STA, n=31). The proportion and absolute number of peripheral blood lymphocyte subsets in each group were measured by flow cytometry and the proportion and absolute count of peripheral blood lymphocyte subsets in each group compared. Results:The proportion and absolute number of CD19 + B cells were markedly lower in BKVN group than those in AR group ( P=0.005, 0.003; 8.5% vs 13.2%, 0.094×10 9/L vs 0.202×10 9/L) and STA group ( P=0.005, 0.003; 8.5% vs 14.8%, 0.094×10 9/L vs 0.198×10 9/L); the proportion of CD3 + CD8 + T cells was significantly higher in BKVN group than that in AR group ( P=0.013; 36.9% vs 31.2%). In addition, no obvious difference existed in the proportion and absolute number of lymphocytes, CD3 + T, CD3 + CD4 + T and CD16 + CD56 + natural killer (NK) among three groups ( P>0.05). No obvious difference existed in the proportion of CD3 + CD4 + / CD3 + CD8 + T cells among three groups ( P>0.05). Conclusions:No difference exists in T cell-related lymphocyte subsets between BKVN and acute rejection recipients. However, the number and proportion of CD19 + B cells decrease markedly in BKVN.