Viral infections are a well known complication in transplant recipients. BK Virus (BKV) belong to the polyomavirus family of double stranded non-enveloped DNA viruses. BK nephropathy is an important cause of renal transplant dysfunction, especially in patients with high levels of immunosuppression. Up to 85 percent of adults have reportedly serologic evidence of exposure to the virus, suggesting the presence of asymptomatic, latent infection. Between January 1985 and August 2008, 325 kidney transplantations were performed in children under 15 years of age. Immunosuppressive medications consists of prednisolone, Cyclosporin A and Mycophenolate Mofetil. BK Virus was detected in urine of 103 of these patients who were in regular follow-up by Polymerase Chain Reaction (PCR) and in blood if patient was symptomatic. Decoy cells were also tested in symptomatic patients. Herein we present our experience in BK Virus Nephropathy in renal transplant children in Labbafinejad Hospital. BK Virus particles were detected in urine of 14 transplant children of whom 3 patients had Decoy cells in pathologic examination of urine and a dramatic rise in plasma creatinine. PCR examination of blood for BK Virus was positive in only one of these patients. Immunosuppressive medications were reduced as first step of treatment but was effective in 2 patients presenting with reduction of creatinine. Cidofovir was used for third patient which was partially effective leaving a plasma creatinine of 1.9 mg/dl. BK Virus Nephropathy should be considered as a cause of each allograft dysfunction in transplant children.