A series of aromatic diamines having ether and/or carbonyl moieties in their structures were synthesized. By using these synthesized diamines and commercially available tetracarboxylic dianhydrides, various kinds of polyimides having ether and/or carbonyl moieties were synthesized. The thermo-oxidative stability of the obtained polyimides was investigated by focusing on the chemical structures of their repeating structure units. The reason for the improved thermo-oxidative stability of the ether-carbonyl polyimide structure was explained by an electronically balanced condition, i.e., the balance of electron donor moiety (-O-) and electron acceptor moiety (-CO-) in a chemical structure, and the degree of electron deficiency of the benzene-imide ring structure. The possibility of the formation of a charge transfer complex (CT-complex) was also mentioned as an explanation of the improved thermo-oxidative stability of ether-carbonyl polyimide structures.