Renal abscess, a very uncommon renal disease in the pediatric patient is often complicated by irrelevant antibiotics treated urinary tract infection or due to other unknown reasons. In this paper, two cases of renal abscess were reported though they had been treated with antibiotics. The diagnosis had been made soon by sonography and computed tomography (CT). In addition, during the period of treatment, a series of sonography were performed to monitor resolution of abscess. In one, the lesion was resolved by antibiotics alone for 2 months duration, the other nearly disappeared 3 weeks later after antibiotics treatment combined with tube-drainage. These imaging techniques permit a prompt diagnosis as well as percutaneous drainage performed if antibiotic treatment dose not lead to resolution of the abscess.