The positron annihilation lifetime (PAL) experiments have been conducted on pure polyether sulfone (PES) and sulfonated polyether sulfone (SPES) with varying degrees of sulfonation, that is, varying ionic exchange capacities (IEC=0.0, 0.75, 1.02, and 1.40 meq/g) at room temperature. In addition, Doppler broadening of annihilation radiation (DBAR) measurements were performed simultaneously with PAL experiments. As IEC increases, the ortho-positronium (o-Ps) lifetime τ3 declines until it reaches 0.75 meq/g, indicating a free volume size fall before leveling off. Conversely, the o-Ps intensity I3 falls off linearly as IEC rises, which could be because SO3H inhibits positronium formation. The free volume sizes and distributions, calculated from the PALs spectra in sulfonated PES samples, reflected the relation between the free volume hole and the IEC. Sulfonated PES polymer has smaller free volume hole size and its distributions are narrower than unsulfonated PES. Sulfonated PES with SO3H makes the S- (W-) parameters, deduced from DBAR, decrease (increase) linearly with increasing the IEC. The S-parameter decreases with the decrement of the Ps fraction corresponding to decreasing I3. The S- and W-parameters correlation shows linear dependence indicating that they have the same free volume or defect structure although their IECs differ. The use of PALS to investigate the free volume and structure of these polymers is made possible by the advantageous production of Ps.