The incidence of symptomatic thrombosis of umbilical arterial catheterization is 1-3%. Therapeutic options may include: using heparin or low molecular weight heparin, using a thrombolytic agent, or surgical thrombectomy. However, there are insufficient data to recommend any one treatment over the others. Recently, enoxaparin, a low molecular weight heparin, has emerged as a drug of choice for the treatment of neonatal thrombosis due to pharmacologic stability over unfractionated heparin or thrombolytic agents. We report a case of successful treatment of aortic thrombosis after umbilical arterial catheterization with enoxaparin in preterm infants.