The crystal structure of diflunisal, 2`, 4`-difluoro-4-hydroxy-3-biphenyl-carboxylic acid, was determined by single crystal X-ray diffraction technique. The compound was recrystallized from a mixture of acetone and water in monoclinic, space group C2/c, with a = 34.666(6), b = 3.743(1). c = 20.737(4) Å, β= 110.57(2)˚, and Z = 8. The calculated density is 1.324g/g/㎤. The structure was solved by the direct method and refined by full matrix least-squares procedure to the final R value of 0.045 for 1299 observed reflections. It was found that the molecules in the crystal are partially disordered. that is, the two equivalent conformers (180˚ rotated ones through C(1)-C(7)) are packed alternatively without regular symmetry or sequence. The two phenyl rings of the biphenyl group is tilted to each other by the dihedral angle of 43.3˚. The carboxyl group at the salicylic moiety is just coplanar to the phenyl ring, and the planarity of this salicylic moiety is stabilized by an intramolecular hydrogen bond of O(3)-H(O3)…O(2). The molecules are dimerized through the intermolecular hydrogen bonds at the carboxy1 group in the crystal.