Aquaporin 3 is a water channel protein. Aquaporins are a family of small integral membrane proteins related to the major intrinsic protein (MIP or AQP0). Aquaporin 3 is localized at the basal lateral membranes of collecting duct cells in the kidney. In addition to its water channel function, aquaporin 3 has been found to facilitate the transport of nonionic small solutes such as urea and glycerol, but to a smaller degree. 

Aquaporin 3 is found in the basolateral cell membrane of principal collecting duct cells and provide a pathway for water to exit these cells. In kidney, AQP3 gene expression is not regulated by vasopressin (ADH). This protein is also a determinant for the GIL blood group system.