Abstract:[Objective] To evaluate the clinical outcome of cup-on-cup technique used in revision surgery for acetabular componentloosening with AAOS IIb acetabular bone defect. [Methods] A retrospective study was performed on 22 patients who underwent revisionhip arthroplasty by cup-on-cup technique in our hospital from February 2016 to April 2017. The clinical and radiological data were evalu-ated. [Results] All patients had the revision THA performed successfully, without vascular, nerve injury and other serious complications,and followed up for (5.3±1.1) years on an average. Compared with those preoperative, the Harris score [(45.5±10.3) vs (90.4±10.6), P<0.05],hip flexion-extension range of motion (ROM) [(78.2±13.6)° vs (103.3±20.4)°, P<0.05], hip internal-external rotation ROM [(26.1±10.7)° vs(46.6±17.9)°, P<0.05], pain VAS score [(8.3±1.3) vs (3.1±0.4), P<0.05], and the leg length discrepancy [(15.1±2.5) mm vs (4.4±1.6) mm, P<0.05] improved significantly at the latest follow up. Radiographically, compared with those preoperatively, both the vertical deviation of thecenter of rotation (COR) [(47.2±10.5) mm vs (20.5±5.7) mm, P<0.05], and the transvers deviation of COR [(15.5± 8.4) mm vs (4.8±3.5) mm,P<0.05] significantly reduced at the latest follow-up. [Conclusion] The preliminary clinical consequence of cup-on-cup technique is satis-factory for AAOS IIb acetabular defect.