Aquaporins are the water channel that facilitate water transport across plasma membrane. In human, there are 13 AQPs, at least one of which is found in every organ system. Recently, it is getting clear that AQPs regulate not only water metabolisms, but also various cellular functions, such as growth and migration. We have found that AQP5, a major isoform in lung epithelia, enhances TNF-α-induced-chemokine expression, but suppresses the response to Th2 cytokines in vitro. It has also known that the expression of AQP5 is markedly reduced in mice with asthma, suggesting that the change of expression level of AQP5 may contribute to the pathogenesis of inflammatory respiratory disease. In this study, therefore, we have established a transgenic (Tg) mouse in which AQP5 is highly expressed specifically in the lung epithelial cells, and examined Th2 inflammatory responses in a model of asthma. In the Tg-mice, the inflammation, assessed by cells in BALF and chemoattractant expression, was considerably less than that in wild type mice, whereas mucus production was increased in Tg-mice. Additionally, mRNA expression of Th2 cytokines were decreased in Tg-mice. Our results indicate that AQP5 can suppress allergic inflammation in vivo, and suggest that decreased expression of AQP5 may suppress the development of inflammatory pathology.