Three perovskite oxynitride solid solutions Ca1–xSrxNbO2N, CaNb1–xTaxO2N, and SrNb1–xTaxO2N were prepared by low temperature ammonolysis of soft‐chemistry precursors. In particular, we present for the first time a way to synthesize the substitution series Ca1–xSrxNbO2N, which cannot be prepared by ammonolysis of classical solid state precursors. All samples were phase‐pure and exhibit bandgaps in the visible light range that can be tailored by substitutions both of the A‐ and B‐type cations. Rietveld analysis was applied to determine cell parameters and crystal structures. In the case of Ca1–xSrxNbO2N a structural change from orthorhombic to tetragonal was found. After loading with CoOx the photocatalytic activities in the solution‐based methyl orange degradation were investigated and for SrNb1–xTaxO2N a considerable activity was found.