A series of polyacylhydrazones having the following structure was synthesized: The glass transition temperatures (T_g's) of the polymers decreased with the increase of m numbers in -(CH₂)_m-among polymers having the same R. The polymers having the m-phenylene group showed higher T_g's than those having the tetramethylene group if the m number in the -(CH₂)_m-group was the same.