The rheological properties of diblock ionomers based on polystyrene-b-poly(sodium methacrylate) (PS-b-PMANa) were studied. Comparing the melt rheology of the block ionomer with that of the star-shaped polymer, it was seen that the viscoelastic properties of the diblock ionomer could be attributed to the same molecular motion as those of star polymers, since the PS-b-PMANa forms micelles that persist even in the melt because of the strong association of the ionic blocks, The dynamic viscoelastic functions of the block ionomer suggested the existence of an additional relaxation at low frequencies. The additional relaxation was thought to be due to the thermal rotational diffusion of the micelles, restricted by the retraction process of polystyrene block chains. The estimated relaxation time was in good agreement with that found experimentally. An alternative explanation of the additional relaxation was based on the possible action of the micelles as a filler, since the rheological behavior of the diblock ionomer at low frequencies was similar to that of a suspension.