The title compound, Mn(4)(H(2)O)(4)[Ge(OH)(2)(HPO(4))(2)(PO(4))(2)], was synthesized by the solvothermal method. Its crystal structure is isotypic with the iron and cobalt analogues [Huang et al. (2012 ▶). Inorg. Chem.51, 3316-3323]. In the crystal structure, the framework is built from undulating manganese phosphate sheets parallel to (010) inter-connected by GeO(6) octa-hedra (at the inversion center), resulting in a three-dimensional network with eight-membered ring channels into which all the protons point. The undulating manganese phosphate sheet consists of zigzag manganese octa-hedral chains along [10-1], built from MnO(4)(OH)(OH(2)) octa-hedra and MnO(5)(OH(2)) octa-hedra by sharing their trans or skew edges, which are inter-connected by PO(3)(OH) and PO(4) tetra-hedra via corner-sharing. The crystal structure features extensive O-H⋯O hydrogen-bonding inter-actions.