The nematic liquid crystalline property of 4-benzoyloxybenzoic acid (BBA) was observed by polarizing microscopy and X-ray diffraction. The structure of the hydrogen-bonded BBA dimer was verified by FT-IR, and the axial ratio (l / d) of the rod-like molecule was calculated to be 5.8, which is large enough to exhibit a liquid crystalline phase. The mesophase was stable at 240 C. At higher temperatures, for example, 270 C, the trans -esterification side reaction occurred. The binary phase diagram of BBA and 4-acetoxybenzoic acid shows the eutectic temperature at 175 C.