Aromatic alternating copolyimides have been synthesized by the reaction of various precursors for imido diamine with 6FDA. The alternating copolyimides appeared to have enhanced solubility in organic solvents such as N,N-dimethylacetamide (DMAc), N-methylpyrrolidinone (NMP), and dimethyl sulfoxide (DMSO) when compared with the corresponding random isomers. Various NMR experiments including 2-D COSY spectra have been performed for the characterization of the alternating copolyimides. On the basis of the NMR results, the synthetic pathway of the aromatic copolyimide through the reaction of a precursor for imido diamine with a dianhydride leads to a copolymer with a complete alternating sequence without randomization during the cyclization reaction. The glass transition temperatures of the alternating copolyimides obtained by DSC measurements showed values similar to those of the corresponding random ones. The decomposition behavior obtained by TGA exhibited close degradation temperatures of the alternating copolyimides regardless of the monomers used.