The ability of water-soluble ammonium-based zwitterions (ZIs) to form aqueous biphasic systems (ABS) in presence of salts aqueous solutions is here disclosed for the first time. These systems are thermoreversible at temperatures close to room temperature and further allow the design of their thermal behavior, from an upper critical solution temperature (UCST) to a lower critical solution temperature (LCST), by increasing the ZIs alkyl chains length. The investigated thermoreversible ABS are more versatile than typical liquid-liquid systems, and can be applied in a wide range of temperatures and compositions envisaging a target separation process.