A new layered aluminophosphate [C6H21N4][Al3P4O16] has been synthesized solvothermally by using triethylenetetramine (tetam) as the structure-directing agent and ethylene glycol as the solvent. The structure of the compound was solved by singlecrystal X-ray di4raction analysis. [C6H21N4] [Al3P4O16] crystallizes in the monoclinic space group P21/c with a59.550 (1), b524.064 (1), c59.601(1)As, b597.99 (1)3, V52184.9 (1) As 3 and Z54 (R50.057 and Rw50.052), and its structure consists of [Al3P4O16]3- macroanionic sheets stacked in an AAAA sequence. As primary building units in the individual sheet, alternating PO4 with terminal P5O and AlO4 tetrahedra are corner-shared to form elliptical eight-membered rings as well as four- and six-membered rings. The macroanionic sheets are held together through H bonds between the terminal P5O groups in the inorganic layers and the N atoms of the tetam molecules, which are triply-protonated.