Transport processes of N(CH3)(4)(+) and Na+ ions in sulfonated polyimide (sPI) ionomer membranes have been studied using three different techniques: pulsed field gradient NMR, a method using radiotracers, and conductivity. For N(CH3)(4)(+), the self-diffusion has been measured in the direction of membrane surface (parallel) and in the perpendicular direction (transverse), whereas for Na+ only transverse self-diffusion has been measured. The effects of the equivalent weight and the length of the hydrophobic and hydrophilic sequence of the copolymer have been investigated. The length of hydrophilic sequence seems to have no influence on parallel diffusion and only a weak influence on transverse diffusion. The equivalent weight influences only transverse diffusion, albeit in a strong way. These effects are also observed in the conductivity experiments. The transport results testify to a multiscale foliated structure of the sulfonated polyimide ionomers.