Proton-conducting oxides based on lanthanum ytterbates (LaYbO3) have been proposed as promising electrolytes due to their high chemical stability in aggressive atmospheres. To improve the transport properties of LaYbO3, a strategy of oxygen deficiency creation by acceptor-type doping is usually employed. However, the acceptor-doping strategy has some limitations related to the low solubility limit of the introduced dopants. To further improve the ionic transport of already doped LaYbO3, two strategies—isovalent doping (chemical factor) and sintering temperature (technological factor)—are deliberately used in the present work. The La0.9Sr0.1Yb0.8R0.2O3–δ (R = In, Er, Y, Dy) were synthesized using the standard citrate-nitrate technology. X-ray diffraction analysis showed that all the samples are single-phase and have an orthorhombic structure with space group of Pna21. Increasing the sintering temperature from 1400 to 1500 °C almost doubles the average grain size of the samples; as a result, the ceramics sintered at 1500 °C have higher grain boundary and total conductivities than those of the ceramics sintered at 1400 °C. Among the La0.9Sr0.1Yb0.8R0.2O3–δ ceramics sintered at 1500 °C, the Dy-substituted material exhibits the highest grain boundary and total conductivities that confirms dopant type affects the electrolyte microstructure which, in turn, affects its electrochemical response. Therefore, the La0.9Sr0.1Yb0.8Dy0.2O3–δ composition can be considered the most conductive among the studied series.