Optical absorption and reflectance spectroscopy have been used to monitor the photochemical reactivity of Ba1−xSrxTiO3 solid solutions with aqueous solutions containing methylene blue. Atomic force microscopy indicates that methylene blue is reduced on the surfaces of domains that have a positive surface polarization. The results indicated that SrTiO3 and BaTiO3 have similar reactivities. As the second component is added to either of the pure materials, the reactivity decreases. However, there is a sharp maximum in reactivity at the tetragonal-to-cubic phase boundary. This is attributed to the anomalously high dielectric constant at this composition that increases the width of the space charge region and charge carrier separation in the near surface region.