INTRODUCTION: Cerebral abscess can result from bacterial meningitis, and is often accompanied by clinical symptoms including fever, lethargy, and seizures, and also abnormal laboratory findings related to systemic inflammatory reaction. S. marcescens has increasingly known as a causative organism of infection in preterm infant in neonatal intensive care unit (NICU). CASE: A female infant was born by an emergent Cesarean section because of the fetal distress at the gestational age 31 weeks and 1 day. The birth weight of the baby was 1,060 g, and was treated in the NICU. The baby showed regular weight gain and reached full enteral feeding at 24 days. There were no specific findings in periodic ultrasonography (US), but on follow-up examination performed on 36 days, a huge hematoma-like mass was observed in the right temporoparietal area (5x5x4 cm). There was still no evidence of distinctive features suggesting the systemic infection in clinical and laboratory findings including culture studies of the patient. And also there were no changes in the images according to the time interval in the follow-up US performed 2 weeks later. In the MRI at 50 days of age, a huge necrotic cyst mass (6x5x5 cm) suggesting abscess or tumor was observed in the right parietal lobe of the brain. So US-guided drainage was performed at the bedside, and pus-like fluid was drained about 10cc, and S.marcescens was isolated in the culture of specimens. In the subsequent lumbar puncture, CSF examination showed a mild pleocytosis (22/μL), an increased protein level (231 mg/dL), and a decreased glucose level (33 mg/dL), but the bacteria did not grow in the culture. Several additional drainages for the abscess were performed and the patient was discharged after 6 weeks of treatment with cefotaxime. Follow-up MRI was showed the improvement of the lesion. CONCLUSION: We report a case of asymptomatic cerebral abscesses caused by S.marcescens, mimicking hematoma and tumor, in the preterm infant.