Right-sided endocarditis rarely occurs in healthy young children and majority of cases involve tricuspid valve. Here we report a case of Eustachian valve endocarditis in a girl with structurally normal heart. The girl was transferred for prolonged fever for 11 days and pneumonia. Breathing sound was decreased on left lower lung field and the chest X-ray revealed pneumonic infiltration on left lower lung. Initial laboratory finding revealed positive Mycoplasma pneumonia Ig M titer (6.6) and Ig G titer (22.5). Although she has no history of congenital heart defect, she underwent echocardiogram (ECHO) to evaluate any focus of fever. On ECHO, there were 2 mass in right atrium (RA) which was sized 10mm and 8mm each. The mass was attached with stalk to the opening of Eustachian valve. Chest CT was done for further evaluation of the pneumonia and the mass in RA which also revealed irregularly shaped, hypoattenuated lesions in RA. The fever sustained for 21 days and she underwent to right atriotomy and removed the mass in RA. Operative finding revealed that 2 masses in RA were attached to multiple, twisted and thin stalk to the opening of Eustachian valve. The pathologic finding revealed the fibrinoid necrotic materials with inflammatory exudates. Blood culture did not reveal any of organism including anaerobic organism and fungus. The fever was subsided after the surgery and discharged after adequate antibiotic treatment for 2 more weeks. Although, pneumonia with Mycoplasma pneumonia infections is very common, endocarditis from Mycoplasma pneumoniae is rarely reported. Physician should be aware of possibility of endocarditis in patients who have prolonged fever from Mycoplasma infections.