[en] Monophase YbB₁₂ samples have been used to determine the magnetic properties, the lattice parameter and the displacement of the K-series X-ray lines of YbB₁₂ relatively to three-valent reference compound YbF₉. Ytterbium in the dodecaboride is shown to have a three-valent state in its hexaboride ytterbium is two-valent