Al(POa)a crystallizes in the monoclinic space group Ic with a=10"423, b=18"687, c=9"222 A, fl= 81.63°; Z= 12. In the [010] direction a subcell structure is present with a period of b/3. The structure was solved from the Patterson function. It can be described as a network of A1 octahedra and P tetrahedra. Infinite chains of tetrahedra run along [001] interconnected by octahedra, the repeat distance in the chain being six tetrahedra. The mean A1-O distance in the octahedra is 1.884 A; the P-O bonds which are linked to octahedra have a mean value of 1.483 A; those connected to other tetrahedra are 1.577 A.