Polyhydroxyamides derivatized with alkyl ester groups were investigated as possible candidates for new heat-resistant fiber materials which could be converted to polybenzoxazoles under fire conditions. Model compounds for these polyhydroxyamides were synthesized and their cyclization chemistry was investigated. The model compound study revealed that all the alkyl ester group containing model compounds could cyclize on heating. The rates of cyclization were dependent upon the structures of substituents. The longer and the larger the substituent, the faster was the rate of cyclization. The polyhydroxyamides showed similar results, namely, polyhydroxyamide derivatized with a longer or larger alkyl substituent showed a faster cyclization rate.