The title compound diphenylphosphinic acid was structurally characterized by single crystal X-ray diffraction analysis. The crystals are monoclinic, space group P21/c with a = 11.474(2), b = 6.0506(12), c = 15.718(3) angstrom, alpha = 90, beta = 99.93(3), gamma = 90 degrees, V = 1074.9(4) angstrom(3), Z = 4, F(000) = 452, D-c = 1.342g/cm(3), mu = 0.230mm(-1), the final R = 0.0429 and wR = 0.1192. A total of 10494 reflections were collected, of which 2545 were independent (R-int = 0.0533). In the crystal packing diagram, intermolecular OH center dot center dot center dot O hydrogen bonds stabilize the solid state of the title compound.