Management of renal transplant patients requires periodic measurement of renal function especially in early post transplant period. This is usually assessed by measuring the creatinine clearance, but because of its limitations, it is not an ideal marker for assessing the renal function. Serum Cystatin C (sCyC) appears to be an endogenous marker of glomerular filtration rate (GFR). To assess the use of sCyC as a marker of renal function in kidney transplant patients, we compared it with serum creatinine (sCr) and creatinine clearance (CrC) in 24-hour urine specimen in the first week post-transplantation. Among 60 patients (62.8% men, 37.2% women) undergoing kidney transplantation (average age: 44.87 ± 13.37 years), we determined serum Cystatin C at 1, 3, 5, and 7 days after kidney transplantation: sCr (using the Jaffe colorimetric method), sCyC (ELISA method), and Cr clearance with a 24 hours urine specimen. During the first 5 days following transplantation, there was a progressive decline in sCr levels. In the first 5 days, post transplantation we could not find good correlation between CrC and sCyC, and the sCyC increased during these 5 days, but after that in day 7, there was a good correlation between CrC and sCyC which is coinciding with decreasing the dose of steroid (R= .625) . Therefore, we recommend using sCyC as a marker of renal function after one-week post kidney transplantation, because it is easier to perform and does not affect by diet and muscle mass.