The random copolyesters (PET-PHB) of Polyethylene terephthalate with different amounts of p-acetoxybenzoic racid have been investigated by several methods sueh as po-larizing microscopy，scanning electron microscopy，X-ray diffraction，DSC，etc.，The experimental results show that the nematie liquid crystal begins to appear at the com-position of copolyester 30(mol)％ PHB，and at which the reek beeomes turbid．Further-more，an abrupt change can be found in the composition dependence of quenehed-melt density

equilibrium melting point，the extant of super-cooling or the extent of super-heating．And it can be related to the onset of liquid crystallinity．It has been proposed that the duple beliees with reversed tail-to-head PHB-PHB segments exist in liquid erystal and arrange in a nematic pattern．