A new superabsorbent copolymer, poly(sodium acrylate-co-sodium 1-(acryloyloxy) propan-2-yl phosphate) [P(SA-co-SAPP)], was synthesized by a novel prepared monomer, 1-(acryloyloxy) propan-2-yl phosphoryl dichloride. The swelling properties of the superabsorbent were investigated by comparison with poly(sodium acrylate) (PSA) and the copolymer of poly(sodium acrylate-co-2-hydroxypropyl acrylate) [P(SA-co-HPA)]. The results showed that (1) the superabsorbent containing sodium 1-(acryloyloxy) propan-2-yl phosphate had higher water absorbency at general testing conditions; (2) the swelling properties of P(SA-co-SAPP) and PSA were obviously influenced by pH of solutions, which were different from that of P(SA-co-HPA); (3) the swelling process and the saturated water absorbency of all superabsorbents were remarkably affected by cations, especially multivalent ones, while barely affected by anions.