Abstract: The aim of this study was to evaluate the incidence and risk factors of umbilical catheter associated thrombosis in newborn infants using color Doppler. In this analytic-descriptive study, 256 newborn infants with umbilical catheters were evaluated during a 15 month. Color Doppler ultrasonography was employed for detection of vascular thrombosis associated with the umbilical catheter placement in the first 24-48 h after admission, weekly until discharge and 72 h after discharge. Among 256 newborns, 12 cases (4.7%) had vascular thrombosis. The rate of thrombosis was 6.9 and 5.7% in the umbilical artery and vein catheters, respectively. Umbilical catheters is accompanied with the risk of thrombosis. Color Doppler ultrasonography is a good way for diagnosis of this thrombosis.