Polyhydroxyamides(PHAs) having dimethylphenoxy and/or alkoxy pendant group were synthesized by condensation polymerization at room temperature for flame retarding applications. The resulting polymer precursors were characterized by FT-IR and 1H-NMR. PHAs were converted to polybenzoxazoles by thermal cyclization reaction. This reaction was highly endothermic and it was studied by TGA and DSC. To observe the cyclization condition of the polymer precursors, they were annealed in a muffle furnace under vacuum at various temperatures for 3 h. The polymer precursor having a dimethylphenoxy pendant group was the only one that was fully cyclized at the lowest temperature, 250 ℃. In case of the polymer having dialkoxy side chains, the polymer with a longer alkoxy chain was fully cyclized at a higher temperature than the polymer with a shorter alkoxy chain. Thus the cyclization reaction can be controlled by the combination of these two pendant groups. By means of wide-angle X-ray diffraction powder patterns, the fully extended alkoxy side chains formed crystalline domains between the layers of the main chains.