We have investigated the influence of Sb incorporation on the effective band gaps and band offsets at InGaAs(Sb)N/GaAs interfaces grown by metalorganic vapor phase epitaxy. Cross-sectional scanning tunneling microscopy and spectroscopy reveal 1.2 eV (1.1 eV) effective band gaps of InGaAs(Sb)N alloys. At the InGaAsN/GaAs (InGaAsSbN/GaAs) interfaces, type II (type I) band offsets are observed. We discuss the relative influences of strain-induced splitting of the valence band and the incorporation of Sb on the band gaps and band offsets at InGaAsN/GaAs and InGaAsSbN/GaAs interfaces.