The differences of thermal properties between rigid rod and flexible bisphenol A (DGEBA) epoxies were studied using modulated differential scanning calorimeter (MDSC), thermal gravimetric analyzer (TGA) and dynamic mechanical analyzer (DMA) techniques. The rigid rod epoxies of azomethine (AM), biphenol (BP) and tetramethyl biphenol (TMBP) were cured with diaminodiphenylsulfone (DDS) and dicyandiamide (Dicy), respectively. The DDS-cured epoxies have higher glass transition temperature (T-g) and decomposition temperature than the Dicy-cured epoxies due to the high functionality and rigid structure of DDS. The AM, BP and TMBP have higher T-g than DGEBA due to the rigid rod structure. The bulky methyl substitution on the BP main chain of TMBP epoxy decreases the order of polymer packing and reduces the T-g. The AM epoxy has the longest rigid rod structure, thus the AM epoxy has a higher T-g than that of BP and TMBP epoxies.