(1-4,HOC6H4NH3)H2PO4, Mr=206.98, Orthorhombic, P2(1)2(1)2(1), a=6.155(2), b=7.514(3), c=18.704(7)angstrom, V=865.9(1)angstrom3,Z=4, D(m)=1.57, D(x)=1.59gcm-3, mu=3.157cm-1, T=298K, R=0.037 (wR=0.027) for 868 independent reflections. The structure was determined by single crystal X-Ray diffraction.It consists of an alternate stacking of (H2PO4)- tetrahedra sheets and (HOC6H4NH3)+ cation sheets. The (H2PO4)-groups are associated to form infinite chains (H2PO4), with internal P-P distances of 4.554(1)angstrom, and are connected to the organic planes thanks to strong hydrogen bonds.