Objective To study the correlation between the post-transplant renal allograft function and the variation of serum cystatin C (CyC) concentration in renal allograft recipients. Methods One hundred and ninety-three renal allograft recipients accepted the same combination immunosuppressive regimen of tacrolimus, mycophenolate and prednisone were enrolled into the study. Patient's serum and urine samples were collected on day 5 post-transplant to detect serum cystatin C, serum and urine creatinine (SCr). Correlation analysis was used to analyze correlation between CyC concentration and SCr concentration or the calculated creatinine clearance rate (CkCCr) by using the Cockcroft-Gault equation and urine creatinine clearance rate (CCr). Specificity and sensitivity of using the CyC concentration to evaluate glomerular filtration rate (GFR) were calculated as well.Results The mean concentrations of serum CyC and SCr on day 5 post-transplant were (1.91±1.2)mg/L and (174.0±129.1)μmol/L, respectively. While the CCr and CkCCr were (67.9±27.3)ml/min and (68.1±27.8)ml/min, respectively. Forty-two patients had a CyC concentration below 1.25 mg/L, 102 patients'CyC concentrations were between 1.25 and 2.0 mg/L and 49 patients'CyC concentrations were above 2. 0 mg/L. As for SCr, 62 patients had a concentration below 125 μmol/L, 83 patients'concentrations were between 125 and 200 μmol/L and 48 patients'concentrations were above 200 μmol/L. For CkCCr, there were 52 cases with a concentration above 80 ml/min, 96 cases with a concentration between 80 and 60 ml/min and 45 cases with a concentration below 60 ml/min. Serum CyC concentration had a negative correlation with CkCCr (r=-0. 907, P＜0. 001) and had a significantly positive correlation with SCr concentration (r=0. 886, P＜0. 001). SCr had a significantly negative relationship with CkCCr (r=-0. 889 ,P＜0. 001). Serum CyC had higher correlation with CkCCr than the correlation between SCr and CkCCr. The ROC curves showed that areas under curve of CyC, SCr, CCr and CkCCr were 0. 877, 0. 771, 0. 832 and 0. 909, respectively. Specificity and sensitivity of CyC, SCr,CCr and CkCCr were 69.3%, 96.1%, 77.1%, 71.3%and 91.6%, 52.2%, 67.5%, 84.6%, respectively.Conclusions Serum CyC concentration elevates earlier than SCr concentration when there is slight renal function impairment. Serum CyC concentration might become a more sensitive marker to evaluate the post-transplant renal allograft function in renal transplant recipients.