Objective To explore the surgical skills of modified Gibson combined with modified ilioinguinal (MGMII) approach in the treatment of Enneking Ⅱ+Ⅲ pelvic malignant tumors in the three-dimensional (3D) printed customized integrated hemipelvic prosthesis, and to evaluate the convenience and accuracy of the surgical approach and the short-term effectiveness. Methods Between January 2017 and March 2019, 7 patients with Enneking Ⅱ+Ⅲ pelvic malignant tumors were treated with tumor resection and 3D printed hemipelvic prosthesis replacement via MGMII approach. There were 6 males and 1 female. The age ranged from 23 to 68 years, with an average of 43.7 years. There was 1 chondrosarcoma, 1 Ewing’s sarcoma, 1 osteosarcoma, 1 malignant Schwannoma, 2 metastatic renal clear cell carcinoma, and 1 metastatic hepatocellular carcinoma. The Enneking stage of 4 cases of primary malignant tumor was stage ⅡB. The disease duration was 6-12 months, with an average of 9.5 months. The preoperative Harris hip score (HHS) was 82.1±1.4 and the Musculoskeletal Tumor Society (MSTS) score was 21.4±1.1. The tumor size by imaging examination was 5.1-9.1 cm, with an average of 6.9 cm. The operation time, intraoperative blood loss, postoperative blood transfusion volume, and postoperative complications were recorded. Postoperative pathological examination confirmed tumor residue according to R classification criteria. The lower limb length, acetabular height, acetabular eccentricity, abduction angle, and anteversion angle were measured and the bone integration was observed by imaging review. Bilateral abductor muscle strengths were measured, and joint function was evaluated by MSTS score and HHS score. Results All operations were successfully completed. The operation time was 210-360 minutes (mean, 280.0 minutes); the intraoperative blood loss was 1 300-2 500 mL (mean, 1 785.7 mL); the postoperative blood transfusion volume was 0-11 U (mean, 6.1 U). Postoperative pathological examination confirmed R0 resection assisted by osteotomy guide plate. All incisions healed by first intention. All patients were followed up 30-48 months (mean, 41.3 months). At last follow-up, the imaging review showed the good osseointegration in all 7 cases. There was no significant difference in the lower limb length, acetabular height, acetabular eccentricity, abduction angle, and anteversion angle between the affected side and the healthy side (P>0.05), all of which met the requirements of anatomical reconstruction. At 3 months after operation, the ratios of muscle strength between the affected side and the healthy side was 68.29%±7.41% at 3 months and 89.86%±2.79% at 12 months, showing a significant difference between the two time points (t=8.242, P=0.000). At last follow-up, the MSTS score and HHS score were 27.3±0.8 and 96.6±1.4, respectively, which significantly improved when compared with those before operation (P<0.05). None of the patients had assisted walking at last follow-up. There was no recurrence, death, or complications such as deep infection, dislocation of the prosthesis, or fracture of the prosthesis or screw. Conclusion MGMII approach can expose the posterior column of the acetabulum, especially the ischial tubercle, which is helpful to avoid tumor rupture during tumor resection and preserve the muscle functions such as gluteus medius and iliac muscle while ensuring the resection scope.