Single-phase Sr₂Bi₂O₅ was formed by calcination of the heterobimetallic complex, Sr[Bi(DTPA)]·9H₂O, at 700 °C for 6 h in air. La-doping by 5 and 10 mol % into Sr₂Bi₂O₅ was also examined. There were no traces of impurity phase in the 5 mol % La-doped Sr₂Bi₂O₅ powder, on the other hand, impurity phases such as Sr₃Bi₄O₉ and SrCO₃ were identified for the 10 mol % La-doped sample. UV–vis spectroscopy revealed that the absorption edge of La-doped Sr₂Bi₂O₅ exhibits red shift as compared to the pure Sr₂Bi₂O₅ and the shift increases with the increase of La³⁺ doping. It was confirmed that the photocatalytic activity of Sr₂Bi₂O₅ for the oxidation of isopropanol is improved with La doping under visible-light irradiation (λ ≥ 420 nm).