Two series of new wholly aromatic thermotropic copolyesters containing the 2-(alpha-phenylisopropyl)hydroquinone (PIHQ) moiety have been synthesized and their basic properties such as glass transition temperature (T-g), melting temperature (T-m), thermal stability, crystallinity, and liquid crystallinity were studied by differential scanning calorimetry (DSC), thermogravimetry (TG), and wide-angle X-ray diffractometry (WAXD) and on a polarizing microscope. The first series was prepared from acetylated PIHQ, terephthalic acid (TPA), and 2,6-naphthalenedicarboxylic acid (NDA), and the second series from acetylated PIHQ, TPA, and 1,1＇-biphenyl-4,4＇-dicarboxylic acid (BDA). The T-g values (152-168 degrees C) of the two series are not much different, although the values for the first series appear slightly higher. The T-m values (287-378 degrees C) and the degree of crystallinity of the first series are appreciably greater than those of the second series. Such differences can be explained by the geometric structure of NDA and BDA moieties. All of the present polyesters are thermotropic and nematic.