The creep behavior of fine-grained La0.8Sr0.2Ga0.85Mg0.15O2.825 (LSGM-2015) was investigated over the temperature: range 1200 to 1300 degrees C in air. The bi ief creep transients, value of the stress exponent close to unity, absence of deformation-induced dislocations, and lack of grain-shape change due to deformation suggest that the creep behavior of LSGM-2015 is controlled by grain boundary sliding accommodated by diffusion. The value of the grain-size exponent close to two indicates that the late-controlling step is lattice diffusion. A comparison of the activation energy for creep with activation energies determined by ionic conductivity, oxygen tracer diffusion, and theoretical predictions reveal that the creep rate of LSGM-2015 is controlled by cation lattice diffusion.