Aim: PI3K/AKT/GSK-3β/β-catenin signaling pathway is a triggering factor for epithelial to mesenchymal transition (EMT) which plays a pivotal role in the pathogenesis of endometriosis. Parthenolide is a sesquiterpene lactone extract that has anti-inflammatory, analgesic and anticancer properties. Hence, we investigated the effect of parthenolide against EMT in the endometrial tissue implants and immortalized epithelial endometriotic cell lines 12Z. Main methods: Twenty- four female Rats with surgically induced endometriosis were treated with parthenolide (2, 4 mg/kg), for 4 weeks. Endometriotic cell line 12Z was used to identify the effect of parthenolide on the wound healing, cellular migration and invasion properties of endometriotic cells. Key findings: Parthenolide decreased the endometriotic implant tissue expression of total PI3K, PI3K-p85, p-AKT, p/total AKT, p-GSK-3β, P/total GSK-3β, and nβ-catenin, as well as increased E-cadherin and decreased vimentin mRNA expression. Parthenolide upregulated PTEN immunoreactivity as well as the endometriotic tissue caspase- 3, caspase-9, BAX levels while reducing Bcl2 level. Additionally, parthenolide decreased endometriotic tissue implants surface area and histopathological score of the epithelial growth. Significance: Our findings showed that parthenolide in a dose dependent manner inhibited PI3K/AKT/GSK-3β/nβ- catenin cascade via enhancement of PTEN with subsequent inhibition of EMT evidenced by elevation of the epithelial marker, E-cadherin and reduction of mesenchymal marker, vimentin, of the endometriotic implants in addition to reversal of invasion and migration properties of epithelial endometriotic cell lines. These findings provide a valuable therapeutic approach for treatment of endometriosis.