The steady-state creep rate of La1-xSrxMnO3 (x = 0.10, 0.15 and 0.25) decreased with increasing Sr content in a regime where diffusional creep is the dominant deformation mechanism. This composition effect when compared to existing point defect models suggested that the rate-controlling species for mass transport in (La, Sr)MnO3 is lattice diffusion of the cations, either lanthanum or manganese. This is in agreement with previous creep (based on an activation energy comparison) and sintering results. Diffusional creep can be used effectively to investigate mass transport in (La, Sr)MnO3.