The crystal structure, magnetic properties, and ion-exchange behavior of RbMnHP3O10 have been determined. The crystal structure (a = 12.1866(3) Angstrom, b = 8.3586(2) Angstrom, c = 9.0763(3) Angstrom, beta = 109.067(1)degrees, space group C2/c), determined from X-ray powder diffraction, is of NH4FeHP3O10 type, consisting of hydrogen triphosphate anions linking Jahn-Teller distorted (MnO6)-O-III octahedra around Rb+ cations. Magnetic susceptibility measurements and low-temperature neutron powder diffraction show that RbMnHP3O10 behaves as a Curie-Weiss paramagnet at high temperatures and orders antiferromagnetically below a Neel temperature of 10 K. The magnetic structure is commensurate with the nuclear cell, and the collinear antiferromagnetic structure has magnetic symmetry group P(c)2/c' with spins of 3.82(6) mu(B) lying in the ac plane. Exchange of H+ for Li+ has not proved possible without a breakdown of the RbMnHP3O10 framework due to strong symmetric hydrogen bonding between triphosphate anions.