MIP family proteins with conserved 6 transmembrane domains can be divided into two groups according to their primary sequences. The CHIP group with deletions is predominant in plant and animal kingdom, and functions primarily as water channels. The GLP group without deletions is minor group with limited prevalence and functions as glycerol transporters. Both prototypes are present in bacteria and evolved separately. CHIP group is further divided into three groups: tonoplast aquaporins, plasma membrane aquaporins, and peribacterial nodulins. The recognition of groups in MIP family will facilitate the search for functional domains and deepen our understanding of this ancient protein family.