Ovarian cancer has a clear predilection to metastasize to the peritoneum, which represents one of the most important prognostic factors of poor clinical outcome. Gonadotropin-releasing hormone (GnRH) receptor is significantly overexpressed during the malignant progression of human ovarian cancer. Here, using lentiviral-based small interfering RNA (siRNA) technology to downregulate GnRH receptor in metastatic ovarian cancer cells, we show that GnRH receptor is an important mediator of ovarian cancer peritoneal metastasis. GnRH receptor downregulation dramatically attenuated their adhesion to the peritoneal mesothelium. By inhibiting the expression of GnRH receptor, we showed decreased expression of α2β1 and α5β1 integrin and adhesion to specific extracellular matrix (ECM) proteins. This was also associated with a reduction of P-cadherin. Furthermore, adhesion of ovarian cancer cells to different ECMs and the mesothelium were abrogated in response to β1 integrin and P-cadherin reduction, confirming that the effects were β1 integrin- and P-cadherin-specific. Using a mouse model of human ovarian cancer metastasis, we found that the inhibition of GnRH receptor, β1 integrin, and P-cadherin significantly attenuated tumor growth, ascites formation, and the number of metastatic implants. These results define a new role for GnRH receptor in early metastasis and offer the possibility of novel therapeutic targets.