Abstract： Objective To investigate the relationship between early-stage renal acute rejection ( AR) and the level of Fractalkine in urine , explore the diagnostic and noninvasive monitoring value in early stage after transplantation by measurement of urine Fractalkine.Methods Urine samples were examined from renal transplant patients between January 2006 and October 2009.A total of 155 patients were enrolled , including 49 with biopsy-proved AR, 58 patients with stable renal function and no abnormal histological findings , 10 patients with subclinical rejection in protocol biopsy , 9 patients with biopsy-proven acute tubular necrosis and 29 patients with biopsy-proven chronic allograft nephropathy.Additionally , urine samples were also collected from 40 healthy controls.Fractalkine was measured in urine samples using a commercial human Fractalkine enzyme-linked immunosorbent assay ( ELISA) kit.Immunohistochemistry for Fractalkine expression was performed on biopsies from renal transplant patients with AR and non -AR.Results Forty-nine patients with AR excreted urinary Fractalkine at a significantly higher level than levels in patients with stable renal function and healthy controls [ ( 429.1 ±56.1 ) vs ( 94.6 ±8.4 ) , ( 84.5 ±8.9 ) ng/mmol creatine,both P<0.001].Patients with AR excreted urinary Fractalkine at a significantly higher level than levels in patients with acute tubular necrosis and chronic allograft nephropathy [(429.1 ±56.1)vs(133.0 ±&nbsp;9.8),(183.0 ±18.9)ng/mmol creatine,both P<0.001].Receiver operating characteristic (ROC)curve was constructed to determine the discriminatory power of Fractalkine levels for diagnosis of AR .The area under ROC curve was 0.920(95% CI:0.875 -0.969,P<0.001), which showed that Fractalkine was a suitable marker for the diagnosis of AR.At a cut-off point of 157.5 ng/mmol creatinine , the sensitivity was 83.7%and the specificity was 84.5% ( P<0.001 ).The dynamic level of urinary Fractalkine in AR patients within 3 weeks after transplantation fluctuated above 300 ng/mmol creatine , which is remarkably higher than patients with stable renal function ( below 200 ng/mmol creatinine ).Conclusions As a noninvasive monitoring method , Fractalkine in urine may be a new approach for detection of AR as well as useful to predict response to antirejection therapy.It has good sensitivity and specificity.Besides, measurement of Fractalkine in urine is a simple , inexpensive method for the routine clinical monitoring after kidney transplantation.