Creep behaviour and dislocation substructure as a function of strain was investigated for two solid solution alloys and the pure components in the KBr-Kl system. The creep characteristics for the KBr-Kl alloys are in good agreement with creep behaviour observed in other ionic and class I metallic solid solution alloys, where the creep rate is controlled by a viscous dislocation glide process. The creep resistance of the KBr-Kl alloys is higher than that for the pure components at the same value of homologous temperature. The dislocation substructure of the KBr-Kl alloys and pure components at large strains consists of well defined subgrains. Subgrain formation is shifted to larger strains in the alloys compared to the pure components as a result of solute drag forces on dislocations during glide.