Abstract: A series of poly(phenylene benzobisoxazole-co-ethylene naphthalate benzobisoxazole)s containing different components of naphthalene were synthesized by copolycondensation of naphthalene dicarboxylic acid,terephthalic acid and 4,6-diamino dihydrochloride.FT-IR,X-ray diffraction,UV-visible absorption spectroscopy and molecular fluorescence spectroscopy were used to characterize the polymer morphology,thermo-physical properties and UV fluorescence properties.The results show that polymer chains remain the ordered crystal structure and high heat resistance due to the introduction of naphthalene,and the thermal decomposition temperature of polymer is kept above 550℃,and the char yield at 800℃ is more than 70%.The polymer UV absorption in MSA and fluorescence emission spectra of polymer films exhibits a red shift.