A series of 1-alkyl-3-methylimidazolium amino acid ionic liquids (ILs) [Cnmim][Gly] were studied by molecular simulations based on the all-atom force field. Volume expansivity and heat capacities for [C2mim][Gly] were calculated for validating the force field. Site-to-site and centre-of-mass radial distribution functions were investigated to depict the microscopic structures. It is interesting to find that one [Gly]- anion could catch more than two imidazolium rings, and they may arrange approximately parallel to each other. Moreover, aggregation of the alkyl chains was observed in the ILs with alkyl side chains longer than or equal to C4.