Zwitterionic betaine polymers show excellent ability to suppress nonspecific protein adsorption. In this study, to investigate the detailed mechanisms of their antifouling properties at the atomic level, the solvation structures in the vicinity of carboxybetaine, phosphobetaine, and sulfobetaine moieties are determined in water and n-hexane using radial distribution functions obtained from molecular dynamics simulations. In aqueous solution, water molecules tightly bind to the anionic groups of zwitterionic moieties. In contrast, in pure n-hexane solvent, no significant solvation structures are present near the anionic groups in the zwitterionic moieties, suggesting that n-hexane molecules do not interact with the anionic oxygen atoms. Our results indicate that the anionic groups play a major role in the antifouling properties of zwitterionic moieties.