A hydrolysis-resistant polymer bearing new quasi-choline phosphate (quasi-CP) structures as side groups, poly(2-methacryloyloxyethyl choline methylphosphonate) (PMCPm), was designed and synthesized. Radical polymerization and sub-surface-initiated radical polymerization were used to prepare homopolymer and polymer brush on polymer substrates. Hydrolytic stability and hydrophilicity of the polymer were confirmed by nuclear magnetic resonance and contact angle measurements. Furthermore, the hydration states were investigated using Fourier-transform infrared spectroscopy and differential scanning calorimetry. The similar hydration behavior of PMCPm to poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) sheds light on understanding the interfacial functions of quasi-CP-bearing zwitterionic biomaterials.