Treatment of superomedially displaced acetabular fractures including a quadrilateral surface (QLS) is challenging. We present a surgical technique using an anatomical suprapectineal QLS plate through the modified Stoppa approach and report the availability of this plate to treat this fracture type along with the surgical outcomes. Sixteen consecutive patients (14 men and 2 women) who underwent surgical treatment using an anatomical suprapectineal QLS plate through a modified Stoppa approach for superomedially displaced acetabular fractures between June 2018 and June 2020, were enrolled retrospectively. These fractures included 11 both-column fractures and 5 anterior-column and posterior hemitransverse fractures, which were confirmed on preoperative 3-dimensional computed tomography. Surgical outcomes were clinically assessed using the Postel Merle d’Aubigné (PMA) score and visual analog scale (VAS) score at the final follow-up, and radiological evaluations were performed immediately after the operation and at the final follow-up. For comparative analysis, 23 patients who underwent internal fixation with the conventional reconstruction plate through modified ilioinguinal approach between February 2010 and May 2018, were selected. This control group was composed of 18 both-column fractures and 5 anterior-column and posterior hemitransverse fractures. The follow-up period was at least 1 year in all patients. The mean operation time and blood loss was 109 min, and 853 ml, respectively, whereas 236 min, and 1843 ml in control group. Anatomical reduction was achieved in 14 (87.5%) patients, while imperfect reduction was achieved in the remaining 2 patients. At the final follow-up, radiographic grades were excellent, fair, and poor in 14 patients (87.5%), one, and one, respectively. The mean PMA score was 16.1 (range 13–18) and the mean VAS score was 1.0 (range 0–3). No secondary reduction loss or implant loosening was observed. However, 2 patients underwent conversion to total hip arthroplasty (THA) due to post-traumatic arthritis and subsequent joint pain. No other complications were observed. In the comparative analysis, radiological outcome showed a significant relationship with the conversion to THA (p = 0.013). Shorter operation time and less blood loss were significantly observed in the QLS plate fixation group through the modified Stoppa approach compared with the conventional reconstruction plate fixation group through modified ilioinguinal approach (p < 0.001, respectively). Simultaneous reduction and fixation using an anatomical suprapectineal QLS plate through the modified Stoppa approach may be a viable technique in superomedially displaced acetabular fractures along with shorter operation time and less blood loss.