Background <p>EMS (Endometriosis) is characterized by the presence of functional endometrial tissue outside the uterus and is one of the most common gynecological disorders. SOX18 (SYR-related high-mobility group box 18) is a transcription factor whose expression is higher in ectopic endometrial tissues than in eutopic endometrial tissues. However, its role in EMS has not been confirmed.</p> Methods <p>Here, immunohistochemistry (IHC) staining was used to analyze the expression pattern of SOX18 in EMS. Next, the effects of SOX18 on cell viability, migration and invasion were investigated. Dual-luciferase reporter assay, chromatin-immunoprecipitation (ch-IP) and DNA pull-down were employed to verify SOX18 binding to the OTUB1 (OTU domain-containing ubiquitin aldehyde binding protein 1) promoter. In addition, co-immunoprecipitation (co-IP) was used to analyze the binding of OTUB1 to YAP1 (Yes-associated protein 1). Allograft mouse model of EMS was established to explore the role of SOX18 in vivo.</p> Results <p>In vitro results demonstrated that upregulation of SOX18 promoted the proliferation, migration and invasion of Ishikawa cells and induced the EMT process, while knockdown of SOX18 showed the opposite effect. In vivo results also confirmed that SOX18 overexpression led to the deterioration of EMS, as reflected by significant pathological changes in mice. Mechanistically, our data proved that SOX18 directly bound to the OTUB1 promoter region and activated its transcription. Further investigation demonstrated that OTUB1 deubiquitinated YAP1 and enhanced its protein stability. Rescue experiments suggested that SOX18 modulated YAP1 expression through upregulating OTUB1, indicating the role of SOX18-OTUB1-YAP1 axis in EMS.</p> Conclusions <p>These discoveries underscore that SOX18 contributes to the pathogenesis of EMS through promoting OTUB1 transcription and activating Hippo/YAP1 signaling pathway, which may provide a new therapeutic target for EMS.</p>