Background: Myxofibrosarcoma (MFS) is a rare subtype of soft tissue sarcoma (STS), accounting for about 5% of STS. At present, the treatment of advanced or metastatic MFS is limited and the prognosis is poor. PD-1/PD-L1 inhibitors have shown efficacy in some subtypes of STS, but there is no real-world research data of MFS. This study retrospectively analyzed the efficacy and safety of PD-1/PD-L1 inhibitors-based treatment for MFS patients in Department of Oncology, Zhongshan Hospital, Fudan University. Methods: Advanced or metastatic MFS patients who underwent PD-1/PD-L1 inhibitors-based treatment were collected. The primary end point of this study was progress-free survival (PFS), and the secondary end points included objective response rate (ORR), disease control rate (DCR), overall survival (OS) and safety. RECIST 1.1 and CTCAE 5.0 were used to evaluate the efficacy and safety. Results: From January 1, 2018 to January 5, 2023, a total of 11 patients were included in the study. The median age was 57 years (27-74 years); 7 males and 4 females; 4 in extremities, 3 in retroperitoneum, each of 1 in pelvic cavity, mediastinum, trunk and head and neck. 3 cases were primarily unresectable or metastatic, and 8 cases were postoperative recurrence or metastasis. Treatment included: 1 case (1/11) with PD-1/PD-L1 inhibitors and chemotherapy, 2 cases (2/11) with PD-1/PD-L1 inhibitors and anti-angiogenesis therapy, and 8 cases (8/11) with PD-1/PD-L1 inhibitors combined with chemotherapy and anti-angiogenesis therapy. 3 patients were administrated with radiotherapy to enhance local control. Chemotherapy drugs included gemcitabine, nab-pacilitaxel, epirubicin/pegylated liposomal doxorubicin, dacarbazine, and eribulin. Anti-angiogenesis drugs included anlotinib and regorafenib. 5 cases were treated in first line, and 6 cases were in second line or above. The median baseline length of target lesion was 12.4 cm (1.7-23.9 cm). Four patients had distant metastasis, including lung, bone, pleura and lymph node. The median follow-up time was 17.6 months. The median PFS was 12.2 months (95% CI: 9-NE), and the median OS was 19.1 months (95% CI: 14.3-NE). The ORR is 27% (3/11) and the DCR is 91% (10/11). The ≥grade 3 adverse events (AEs) were neutropenia (36.4%), fatigue (18.2%) and hand-foot syndrome (9.1%). The most common AEs of grade 1-2 were of neutrophil (45.5%), hypothyrosis (27.3%), nausea (27.3%), numbness (18.2%), fatigue (9.1%), anemia (9.1%), hepatic impairment (9.1%), and arrhythmia (9.1%). No treatment-related death happened. Conclusions: This is the first retrospective study revealed that the PD-1/PD-L1 inhibitors-based treatment had good efficacy and tolerable toxicity in Chinese advanced or metastatic MFS patients. Further prospective clinical trials and biomarker research on forecasting the efficacy of immune checkpoint inhibitors of MFS are warranted.