AbstractThe quaternary selenide, La3Sb0.33SiSe7, was prepared from stoichiometric mixtures of elements by solid‐state reactions at 1223 K in an evacuated silica tube. La3Sb0.33SiSe7 crystallizes in the chiral P63 space group and belongs to the Ce3Al1.67S7 structure type. Its structure features one‐dimensional chains of face‐sharing SbSe6 octahedra running parallel to the c direction surrounded by the discrete SiSe4 tetrahedra and La cations. UV/Vis/NIR diffuse reflectance spectroscopy study shows its optical gap of around 1.75 eV. DFT study indicates an indirect bandgap with an electronic transfer excitation from Se 4p to La 5d orbital electrons.