The adsorption and reaction of acetaldehyde (CH3CHO) on stoichiometric (TiO2-terminated) and reduced SrTiO3(100) surfaces have been investigated using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Acetaldehyde adsorbs molecularly on the stoichiometric SrTiO3(100) surface that contains predominately Ti4+ cations. The Ti4+ sites on the stoichiometric SrTiO3(100) surface are not sufficiently active for surface reactions such as aldol condensation, as opposed to the Ti4+ ions on the TiO2-(001) surface. However, decomposition and redox reactions of acetaldehyde occur in the presence of surface defects created by Ar+ sputtering. The decomposition products following reactions of acetaldehyde on the defective surface include H-2, C2H4, CO, C4H6, and C4H8. Reductive coupling to produce C2H4 and C4H8 is the main reaction pathway for decomposition of acetaldehyde on the sputter-reduced SrTiO3(100) surface.