Lipoblastoma is an uncommon benign lipomatous tumor, occurring typically in children less than 3 years of age. The magnetic resonance image (MRI) is a useful tool for diagnosis of lipoblastoma; its imaging typically shows high-intensity signals on both T1-weighted (T1-W) and T2 weighted (T2-W) images. Here, we present a 12-year-old female patient with a painless mass on the anterior right shoulder. MRI showed the mass with low-intensity signals on T1-W and high-intensity signals on T2-W images. Because of the atypical age and MRI findings, it was difficult to make a conclusive diagnosis of the tumor as lipoblastoma preoperatively. Histopathological examination of the excised tumor showed spindle-shaped or stellate cells embedded in the myxoid matrix, and a few small irregular clusters of mature fat cells that are separated by connective tissue septa. There were some immature, lipoblast-like cells dispersed. These findings are consistent with lipoblastoma, and myxoid liposarcoma was considered as one of the differential diagnosis. We finally diagnosed the tumor as a lipoblastoma for the reasons that there were many mature fat cells and no atypical cells for a myxoid liposarcoma. The postoperative course was uneventful and no recurrence was observed 5 years after the operation. The patient presented is worthy of note due to the unusual characteristics of the tumor. Even in the case of adolescent or older patients with atypical imaging, lipoblastoma should be considered as one of differential diagnosis.