and importance: Pelvic osteosarcoma is quite rare and is a challenging task for orthopedic surgeons. This aim of this study is to present the first case report using customized 3D-printed prosthesis in Vietnam. 57-year-old male was diagnosed with pelvic osteosarcoma. After neoadjuvant chemotherapy, we did limb-salvage surgery after partial pelvic resection. He had to undergo another surgery due to an infection complication that exposed part of the prosthesis. At 6 months follow-up, the patient's overall status was stable. VAS score when moving is 2/10. He can walk with one crutch. Patient is still being followed up and treated. Management of pelvic osteosarcoma remains a challenging task for orthopedic surgeons. Advancements in customized 3D-printed prosthesis have been applied in treatment of pelvic osteosarcoma. Despite the complications, the results are promising. We believe that this is a new and innovative route in surgery of pelvic osteosarcoma. Using customized 3D-printed prosthesis is a good way for management of pelvic osteosarcoma. •Osteosarcoma of pelvis is not common, account for 4–10% of all bone cancer.•Pelvis connect the lower limb with body by hip joint and support the intraabdominal organ.•It is very difficult to preserve the pelvis after wide resection.•Custom made 3D printed implant give us a chance to restore the pelvis anatomically and functionally.