The title compound, lithium trimanganese bis[trioxoselenate(IV)] hexakis[hydrogentrioxoselenate(IV)], is built up from a vertex-sharing network of distorted Mn(III)O(6) octahedra, SeO(3) and HSeO(3) pyramids and unusual Li(OH)(6) octahedra, resulting in a dense three-dimensional structure. Mn, Li and one Se atom have site symmetries of -1, -3, and 3, respectively. An O-H...O hydrogen bond helps to establish the crystal packing.