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Rare-earth fluorine-containing molybdates of the <i>Ln</i>₅Mo₃O_16+δ oxygen–electron conductor family with the LiLa₄Mo₃O₁₅F composition were synthesized for the first time as single crystals by the flux method. An accurate X-ray diffraction analysis of the obtained crystals was carried out at 20 and −183 °C. The LiLa₄Mo₃O₁₅F compound is isostructural to the fluorine-free analogue with a cubic structure (space group <i>Pn</i><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mover accent="true"><mn>3</mn><mo>¯</mo></mover></semantics></math></inline-formula><i>n</i>). It is shown that lithium atoms replace one of the two positions of lanthanum in the more distorted LaO₈ polyhedron. According to X-ray diffraction analysis, fluorine atoms replace the positions of over-stoichiometric oxygen located in the vast cavities of the structure. So, fluorine anions can promote the interstitial conductivity of F-containing LiLa₄Mo₃O₁₅F molybdates.