Bright red crystals of [Mn(H₂O)₆][BiI ₄]₂·2H₂O are obtained from a solution of MnI₂, BiI₃, and I₂ in absolute ethanol, which is exposed to humid air. Reversible dehydratization sets in at about 50 °C. Added water decomposes the hydrate by irreversible precipitation of BiOI. The optical bandgap is about 1.9(1) eV. X-ray diffraction on a single-crystal revealed a monoclinic lattice (space group P2₁/c) with a = 760.39(4) pm, b = 1315.6(1) pm, c = 1398.37(7) pm, and β = 97.438(4)°. In the crystal structure zigzag chains of edge-sharing [BiI_2/1I _4/2]^- octahedra and linear strings of H ₂O-bridged [Mn(H₂O)₆]²⁺ octahedra run parallel [100].