A new layered ammonium cobalt-zinc phosphate has been synthesized under solvothermal conditions at 160 degrees C and the structure solved using room-temperature single-crystal X-ray diffraction data. (NH1[Zn2-xCox(PO4)(HPO4)] (x approximate to 0.12), M-r = 339.75, triclinic, space group P-1, a = 5.237(1) Angstrom, b = 8.944(1) Angstrom(3), c = 9.728(1) Angstrom, alpha = 74.99(1)degrees, beta = 77.64(1)degrees, gamma = 72.92(1)degrees, V = 416.19(1) Angstrom(3), Z = 2, 1.511 observed data measured with I > 3 sigma(I), R = 4.31% and R-w = 4.67%). The structure consists of MO4 (M = Zn, Co), PO4, and PO3(OH) tetrahedra linked to form buckled layers containing three-and four-membered rings between which ammonium cations reside. A network of hydrogen bonds involving both interlayer and layer-to-ammonium interactions holds the phosphate layers together.