A new two-dimensional aluminophosphate layer [Al2P3O10(OH)2][C6NH 8] (compound 1) has been prepared from an alcoholic system using 4-methylpyridine (C6NH7) as a template. The as-synthesized product is characterized by powder X-ray diffraction, dynamic thermogravimetric, and 31P-, 27Al-, and 13C magic-angle spinning (MAS) NMR analyses. The structure has been solved by single-crystal X-ray diffraction analysis. Compound 1 crystallized in the monoclinic space group P21/c (no. 14), with a = 8.686 (3) Å, b = 21.240 (3) Å, c = 8.799 (2) Å, β = 113.23 (3)°, and Z = 4. The inorganic layers are constructed from alternating aluminum units (AlO4 and AlO5) and phosphorus units [PO4, PO3(OH), PO2(=O)(OH)] and are featured by rows of edge-sharing bridged six-membered rings (6MRs) and zigzag four rings (4MRs). The layers are held with each other through strong H-bondings between the terminal oxygens attached to the 2-connected phosphate groups in adjacent layers. The organic ammonium cations (C6NH8+) are located in the large cavities between the interlayer regions. The structural features and relationships in the anionic aluminophosphates with Al2P3O123- stoichiometry, including compound 1 and previously reported compounds, are discussed. Furthermore, new two-dimensional (2-D) networks have been proposed on the basis of the discovered building rules for aluminophosphates with Al2P3O123- stoichiometry.