Early and accurate detection of decreasing glomerular filtration rate (GFR) is critical to prevent early graft rejection in post- transplantation period. Serum creatinine has several drawbacks as a marker of GFR, so serum cystatin C has been proposed as a better alternative GFR marker. We prospectively evaluated the diagnostic value of cystatin C measurements compared with creatinine in the early post-operative phase. In 78 renal recipient patients serum creatinine and cystatin C were measured on the 3rd, 7th and 14th post-transplantation day. GFR was established by creatinine clearance with the cut off at 80 ml/min/1.73 m2. The correlation between serum creatinine and cystatin C with GFR was determined. Sensitivity and specificity of these markers were analyzed by R. O. C procedures. There were 78 renal recipient patients (51 male, 27 female) with the mean age of 34.56± 13.36 years and mean body mass index (BMI) of 22.36± 3.46 kg/m2. Serum cystatin C was not influenced by gender, age and BMI. There was a significant correlation between serum creatinine and cystatin C levels with GFR on 3rd, 7th, and 14th days (P< 0.001). Analysis with R. O. C procedures showed that in detection of decreasing GFR (GFR< 80 ml/min/ 1.73 m2 on the 7th day (P= 0.023, AUC= 0.694). sensitivity and specificity of serum cystatin C was 67.7% and 77.9% respectively on the cut off point of 2264 ng/ml. Cystatin C has good sensitivity to estimate the renal function in the early period of transplantation, but its value as a marker of GFR was decreased at the end of first week.