Aquaporin (AQP) water channels play an important role in fluid homeostasis and the control of epithelial cell volume. To understand the oviductal fluid homeostasis, the expression of aqp5 was examined in mouse oviduct. In the oviduct of cycling females, aqp1, aqp3, aqp4, aqp5, aqp6, aqp7, aqp8, and aqp11 mRNA were detected. Of these, expression of aqp5 mRNA increased significantly from the early prepubertal period to puberty. Epithelial AQP5 immunoreactivity was markedly increased during the same period and was most notable in the infundibulum. In immature female mice (3 weeks old), gonadotropin (pregnant mare's serum gonadotropin (5IU/head) and human chorionic gonadotropin (5IU/head), single intraperitoneal injection) significantly increased oviductal aqp5 mRNA and AQP5 immunoreactivity in oviduct epithelia. In adult mouse oviduct epithelia, AQP5 was primarily found in the apical membrane, subapical cytoplasm and basolateral membrane of secretory non-ciliated cells, whereas weak to negligible immunoreactivity was found in β-tubulin-positive ciliated cells. Taking into account the fact that non-ciliated cells are well developed with subapical secretory vesicles as well as endosomes, AQP5 may also participate in the secretion and endocytosis in addition to water movement through non-ciliated secretory cells. AQP5 immunoreactivity was also found in the isthmic muscle and lamina propria beneath the epithelia. In cycling females, oviductal aqp5 mRNA levels were the highest at oestrus and the lowest at di-oestrus. AQP5 immunoreactivity in non-ciliated cells was notable in the infundibulum, where AQP5 immunoreactivity was relatively high at oestrus but low at dioestrus and pro-oestrus, indicating synchrony between aqp5 gene activation and the ovarian cycle. Together, the findings of the present study indicate that aqp5 specific to non-ciliated cells is activated during sexual maturation, supporting fluid homeostasis in mouse oviduct.