Small cell osteosarcoma (SCO) is the most rare subtype of osteosarcoma and has a poor prognosis. An 11-year-old boy presented with 2-month history of painful tumefaction in the lower leg. Imaging analysis demonstrated a mixture of osteolytic and osteosclerotic lesions in the proximal tibia and extraskeletal area. Histology of the open biopsy showed small round cells producing mucous matrix. Based on these findings, SCO was suspected. The patient received three cycles of neoadjuvant chemotherapy using high-dose ifosfamide, high-dose methotrexate, pirarubicin and carboplatin. Wide-margin resection was performed followed by tibial lengthening using the Ilizarov method and two cycles of adjuvant chemotherapy with the same drugs as for neoadjuvant chemotherapy. Histology of the resected specimen showed that almost all tumor cells were necrotized. Neither recurrence nor metastasis was found after 4 years. Our experience suggests that neoadjuvant chemotherapy, such as the one used here, would be exceedingly effective for SCO without serious non-hematological toxicities.