The capillary flow of a commercial ionomer melt was studied both experimentally and numerically. The excess pressure drop due to entry, the effect of pressure on viscosity and the possible slip effects on the capillary data analysis have been examined. Using a parallel-plate rheometer equipped with a partitioned plate, and a capillary rheometer with a series of capillary dies having different diameters, D, and length-to-diameter L/D ratios, a full rheological characterization has been carried out. The experimental rheological data have been fitted to a viscoelastic (K-BKZ) model. Particular emphasis has been placed on the pressure-dependence of viscosity, with a pressure-dependent coefficientA,. For the viscoelastic K-Bla simulations, the time-temperature shifting concept has been used for the non-isothermal calculations, while the time-pressure shifting concept has been used to shift the relaxation moduli for the pressure-dependence effect. It was found that these viscoelastic simulations were capable of reproducing the experimental data well with significant effects resulting from the effect of pressure on viscosity, a parameter which cannot be neglected for this class of polymers. Moreover the effect of ionic interactions on the pressure drop has been assessed by comparing the results with those of a linear density polyethylene (LDPE) (parent polymer of this ionomer). Although the ionomer has a slightly smaller viscosity, its entry pressure drop is almost double than that of LDPE with vortices stronger and larger. These observations signify the effect of ionic interactions in flows that are presented for the first time in the literature.