A facile one-step method for the synthesis of aliphatic polybenzoxazoles has been developed. Thus, a series of aliphatic polybenzoxazoles having inherent viscosities of 0.2-0.7 dL/g in concentrated sulfuric acid were successfully synthesized by the melt polycondensation of aliphatic dinitriles with 4,4’-diamino-3,3’-dihydroxybiphenyl (AHB) or its hydrochloride (AHB-HC1) with the elimination of ammonia or ammonium chloride, respectively. Monomer AHB-HC1 was more reactive than the parent AHB, thereby affording higher molecular weight polybenzoxazoles in a shorter reaction time. The aliphatic polybenzoxazoles having 6-10 methylene units were highly crystalline with melting temperatures in the range of 187-308 degrees C, which were stable up to 400 degrees C in a melt state in nitrogen.