Based on LaScO3 proton-conducting oxides with a perovskite structure, having high chemical stability to water vapor, are promising proton electrolytes for SOFC, but they are poorly studied in the form of thin films. Lanthanum-strontium manganite is one of the most common materials for the SOFC cathode. The aim of this work is to study the effect of the La0.6Sr0.4MnO3-α cathode substrate composition on the properties of La1-xSrxScO3 (0.01, 0.05 and 0.10) thin-film proton electrolytes, obtained by simple centrifugation of the film-forming solution. The properties of La1-xSrxScO3 in the form of ceramic and thin-film samples are compared. The experiment showed that the films La1-xSrxScO3 at 5-30-fold deposition on cathode substrates form continuous coatings with a grain size of 50-200 nm, which do not contain transverse pores. These results have a fundamental importance for the development of SOFC with ultra-thin film electrolyte on a supporting electrode. Under dry and wet air, the electrical conductivity of La0.6Sr0.4MnO3-α/La1-xSrxScO3/Pt cells is found to be bulk conductivity and to rise with increasing atmospheric humidity which indicates an increase in the contribution of proton conductivity. In this case, the grain-boundary resistance of the material and the polarization resistance of the electrodes are practically not realized. The conductivity of LSS films is 1-2 orders of magnitude higher than the bulk conductivity of ceramic samples of similar composition and has low activation energy. The observed differences in the conductive properties of films are explained by the interaction of related perovskites of the scandate and lanthanum manganite. The data obtained may be of interest to specialists in the fields of hydrogen energy, electrochemistry, materials science, the development of electrochemical devices: sensors and fuel cells.