The proton conduction in single phase La0.6Ba0.4ScO2.8 with a cubic perovskite structure was studied. The endothermic peak in differential thermal analysis (DTA) curve and the weight loss in thermal gravimetric analysis (TGA) one for as-sintered sample were observed between 340 and 410 degreesC during the heating process in dry N-2 atmosphere. These results were due to the dehydration of the water, which might have been incorporated into oxygen vacancies during the cooling process after sintering. In wet N-2 atmosphere (p(H2O) = 6.1 hPa), a plateau of the conductivity data was observed between 450 and 300 degreesC in the plot of log(sigmaT) versus the reciprocal temperature while the conductivity data measured in dry atmosphere decreased linearly over the measured temperature range, implying that proton conduction was dominant below 450 degreesC.