Gardner-associated fibroma (GAF) is a benign lesion of soft tissue which has recently been described and is exceedingly rare in children. GAF is associated with adenomatous polyposis coli gene mutation, familial adenomatous polyposis and desmoid. We report a case of patient with soft tissue tumor on her lower back which was turned out to be GAF. The patient was a 19-month-old female who visited out-patient clinic with palpable mass on her lower back and we performed surgical excision. The tumor was located at subcutaneous and we excised the tumor including surrounding soft tissue. She discharged without any complication on surgery day. The pathologic report showed dense collagenous tissue with spindle cell and adipose tissue, suggestive of GAF. We are planning to check gene study and to perform endoscopy and abdominal ultrasonography for at the age of 4.