A new Mn-rich member in the wyllieite structural group has been synthesized by hydrothermal technique: Na1.265Mn2+2.690Mn3+0.785(PO4)3 (a = 6.5291(6), b = 12.653(1), c = 10.952(1)Å, β = 97.18(1)°, space group P21/c, Z = 4). Its crystal structure was solved and refined against F2 to R = 0.0277. It is based on a cationic framework of Mn octahedra sharing edges. The PO4 tetrahedra strengthen the framework by sharing all vertices with Mn octahedra. Na atoms occupy interstices of the structure and channels parallel to the a axis. Unlike the minerals of the wyllieite family the new phase contains Mn3+ cations in the position usually occupied by Al (or Fe3+).