Aquaporins, water specific conducting channels, ubiquitously exist among animals, plants and microbes. There are six kinds of aquaporins in mammalian plasma membrane, which locate on the organs that participate actively in water metabolism. Plant aquaporins exist both in plasma membrane and tonoplast, which have a general role in regulating transmembrane water transport during the growth, development, and stress responses of plants. Most information about the structure and function of aquaporins comes from those researches on AQP1 that exists in erythrocyte membrane. Aquaporins assemble in the membrane as a homotetramer with each monomer having its individual water conducting function.The distribution of tetramer in membrane is unsymmetrical, which exhibits four protrusions in the inside surface of membrane and forms a large central cavity outside.