Two series of polyimides containing 1,3,4-oxadiazole rings in the main chain, one of them having flexible hexafluoropropane-2,2-diyl groups and the other with carbonyl groups, were prepared by polycondensation of aromatic diamines containing 1,3,4-oxadiazole rings with hexafluoropropane-2,2-diyl-bis(phthalic anhydride) or benzophenonetetracarboxylic dianhydride. Their properties, such as solubility in organic solvents, thermal stability, glass transition temperature, photoluminescence and film-forming properties of the two groups of polymers have been studied and compared.