In attempts to synthesize compounds containing mixed lanthanide and transition metal oxide magnetic nanostructures, a new 3d-4f arsenate phase, Na3GdMn3O3(ASO(4))(3), was isolated using high-temperatore, molten-salt methods. The X-ray single-crptal structure analysis shows that Na3GdMn3O3(ASO(4))(3) crystallizes in a hexagonal space group with a = 11.091 (2) angstrom, c = 5.954(1) angstrom, and V= 634.2(2) angstrom(3); P6(3)/m (No. 176); Z= 2. The structure has been refined by full-matrix, least-squares methods to a final solution with R1 = 0.0466, wR2 = 0.1318 and GOF = 1.101. This new three-dimensional framework consists of ferromagnetic one-dimensional [MnO4](infinity) chains, composed of edge-shared MnO6 units propagating along c. The GdO9 polyhedra connect three neighboring [MnO4](infinity) chains via oxygen atoms. Na3LaMn3O3(ASO(4))(3) (1), and Na3SmMn3O3(ASO(4))(3) (2), the isostructural derivatives of Na3GdMn3O3(ASO(4))(3) (3), were synthesized to acquire additional insight into the 3d-4f magnetic couplings. The Na(3)LnMn(3)O(3)(ASO(4))(3) series reveals an increase in chi T at low temperatures upon substitution of smaller Ln(3+) ions ranging from La3+ to Gd3+. The increase in chi T is likely due to the magnetic nature and size of the lanthanide ions present. It was expected that the Mn-O-Mn ferromagnetic interactions would dominate as 3d-4f magnetic interactions are generally weak. The magnetic data shows that the paramagnetic Ln(3+) ions in 2 (Sm) and 3 (Gd) do significantly enhance the bulk ferromagnetism compared to that of 1 (La), suggesting sizable contributions from the 4f magnetic ions.