Objective To evaluate the surgical procedure of reinforced acetabular cage with caudal flange in reconstruction of pelvic defect after acetabular tumor resection. Methods Between June 2003 and December 2009, 25 patients with Harrington class III pelvic defect underwent reconstruction with a reinforced acetabular cage with caudal flange and total hip arthroplasty (THA). There were 13 males and 12 females with an average age of 51.2 years (range，13-73 years). The main cl inical manifestations included hip pain and buttock pain, with a median disease duration of 6 months (range, 1-96 months). Pathological findings showed 18 cases of metastasis, 3 cases of multiple myeloma, 1 case of non-Hodgkin’s lymphoma, 1 case of grade I chondrosarcoma, 1 case of giant cell tumor, and 1 case of chondroblastoma. For the patient with chondroblastoma, THA with LINK RIBBED system was used. An artificial total hip system made in China was used in 6 patients and LINK SP II system was used in the other 18 patients. Results No patients died perioperatively. Deep infection and hip dislocations occurred in 1 and 2 patients, respectively. At last follow-up, 8 of 18 patients with metastasis died of cancer and the average survival time was 11 months. The other 10 who were al ive were followed up 15 months on average. One patient with multiple myeloma died of pulmonary infection at 21 months after operation and the other 2 with multiple myeloma and 1 with lymphoma were al ive with an average follow-up of 17 months. The patient with grade I chondrosarcoma and patient with chondroblastoma were followed up 58 and 12 months, respectively, without recurrence. Recurrence occurred in the patient with giant cell tumor at 19 months afteroperation. Loosening of implant occurred in 3 patients because of local tumor recurrence. For the 23 patients at 6 months after operation, the mean Musculoskeletal Tumor Society (MSTS) 93 score was 81% (range, 57%-93%). Conclusion Reinforced acetabular cage with caudal flange could be used together with THA for reconstruction of Harrington class III pelvic defects after acetabular tumor resection, and low incidence of postoperative compl ication and good functional outcome could be expected.