This article reports on two novel strontium bismuthate photocatalysts (Sr ₆Bi ₂O ₁₁ and Sr ₃Bi ₂O ₆) prepared by a solid-state synthesis for which the number of strontium atoms exceeds the number of bismuth atoms in the cation sublattice; for comparison, the bismuthate Sr ₂Bi ₂O ₅ was also re-examined. All three bismuthates were characterized by a variety of spectroscopic techniques (XRD, XPS, EDX, DR, Raman, SEM, and EIS). Direct bandgap energies for the three bismuthates were assessed from diffuse reflectance spectra: 2.61 eV for Sr ₆Bi ₂O ₁₁; 3.40 eV for Sr ₃Bi ₂O ₆; 3.17 eV for Sr ₂Bi ₂O ₅, while the flatband potentials (versus NHE) of the corresponding valence bands were estimated from XPS spectra: +2.22 eV for Sr ₆Bi ₂O ₁₁; +1.71 eV for Sr ₃Bi ₂O ₆; +1.61 eV for Sr ₂Bi ₂O ₅. The two novel bismuthates displayed photocatalytic activity toward the photodegradation of acetaldehyde in the gas phase and phenol in aqueous media, with the Sr ₆Bi ₂O ₁₁ system exhibiting significantly greater photoactivity vis-à-vis the Sr ₃Bi ₂O ₆ bismuthate; by comparison, Sr ₂Bi ₂O ₅ was photocatalytically inactive in this case; their photoactivity was also assessed from the photodegradation of phenol in aqueous media (in all cases using UV-Vis irradiation from a Xe light source). Detailed photocatalytic mechanisms are proposed based on UV-induced coloration studies (carried out using a high-pressure Hg lamp; 365 nm) and on the photodegradation in the presence of radical scavengers to explain how composition and structure of the three bismuthates affect their photocatalytic activity. The role of point defects (oxygen vacancies) in their crystal lattice is described as they affect photocatalytic activity by acting as electron traps and potentially as electron/hole recombination centers.