Non-ossifying fibromas usually occur in the metaphysis of the long bones in children, and are extremely rare in the mandible. Here, we present a case of non-ossifying fibromas which occurred in the mandible of a 4-year-old boy. The patient had no complaint of ache. Laboratory blood examination of serum calcium, phosphorus, and parathormone levels was normal. Computed tomography of the maxillofacial region showed a well-defined osteolytic lesion affecting the right mandible. Microscopically, the lesion showed whorled bundles of spindle-shaped fibroblasts, as well as foam cells, mingled with scant multinucleated giant cells, without any bone formation. It is necessary to distinguish non-ossifying fibromas from other giant cell-containing lesions because of the extremely infrequent occurrence of this lesion in the mandible. We reviewed the histologic features of 14 cases of non-ossifying fibromas involved in the jaw.