Previous studies demonstrate significant roles for passive water channels (aquaporins, AQPs) in maintaining water homeostasis in cell membranes of endometrial cells during decidualisation and embryo implantation. However, there is little information regarding the role of AQPs in the human fallopian tube, specifically their role in human tubal ectopic pregnancy. In this study we took tissue samples from the site of implantation of tubal ectopic pregnancy (group 1, N = 30, mean age 32 years, range 23-42) and the corresponding non-implantation site in women undergoing salpingectomy for tubal pregnancy (group 2). Ampullary fallopian tubes during mid-secretory phase were collected as control group (group 3, N = 17, mean age 37 years, range 30-50). Thin sections were prepared and stained with anti-AQP9, and, for estrogen and progesterone receptors in each group. Immunohistochemical studies showed that AQP9 proteins localize in the cytoplasm of epithelial cells of Fallopian tube. Expression of AQP9 was significantly reduced during tubal pregnancy compared to controls (group 1 vs. group 3, P = 0.036; group 2 vs. group 3, P = 0.029), and, this reduced expression was not related to estrogen receptor or progesterone receptor status (group 2, ER vs. AQP9, Pearson r = 0.173, P = 0.361; PR vs. AQP9, Pearson r = 0.124, P = 0.514, respectively). Similarly, there is no correlation between AQP9 and estrogen receptor or progesterone receptor status in the normal group (group 3, ER vs. AQP9, Pearson r = -0.026, P = 0.923; PR vs. AQP9, Pearson r = -0.292, P = 0.255, respectively). Reduced expression of AQP9 in human fallopian tube may contribute to aspects of pathophysiology of tubal ectopic pregnancy.