Abstract: The ¹H spin-diffusion process of a series of polyurethane zwitterionomers was investigated by a modified Goldman-Shen pulse sequence on a solid NMR spectrometer. The Fickian's diffusion equation was solved according to appropriate boundary and initial conditions. The data treatment was greatly simplified by doing some reasonable assumptions and omissions. The domain sizes of two samples with different degree of ionization were obtained and the influence of ionization on the morphology of the samples is discussed.