G-protein coupled receptor 4 (GPR4) is a G protein-coupled receptor (GPCR) activated by sphingosylphosphorylcholine (SPC) and lysophosphatidylcholine (LPC). Later studies indicated that GPR4 can serve as a proton sensor. GPR4 has been known to play a critical role in the tube formation of vascular endothelial cells, and GPR4 overexpression is observed in various types of malignancies, suggesting its involvement in the cancer-related angiogenesis. In this study, we examined the GPR4 expression levels in blood vessels of ovarian cancer, and analyzed the relationship between GPR4 expression and the clinical and pathological characteristics of patients with epithelial ovarian carcinomas (EOC). Results from immunohistochemistry showed that GPR4 is detectable in the endothelium of vessels of both EOC and benign ovarian tumor tissue, but the expression levels were significantly increased in EOC. Moreover the increased expression is accompanied by a higher microvascular density (MVD) in EOC compared to that in the benign ovarian tumors. We demonstrated a positive correlation between GPR4 expression density and MVD in EOC, but not benign ovarian tumor tissues. Further analyses indicated that GPR4 expression and MVD in EOC were correlated to the status of lymph node metastasis and clinical stage, but not significantly correlated to the pathological classifications, histopathological grades, the amounts of ascites, status of peritoneal cytology, tumor sizes, or patients' ages. These results suggested that GPR4 may play an important role in the development of EOC, and its overexpression might be required for the angiogenesis, tumor growth, and metastasis of EOC.