Novel methyl-substituted aromatic poly(ether sulfone)s and poly(ether ketone)s were synthesized from combinations of 3,3’,5,5’-tetramethylbipheny-4,4’-diol and 2,2’,3,3’,5,5’hexamethylbiphenyl-4,4’-diol, and 4,4’-dichlorodiphenyl sulfone and 4,4’-difluorobenzophenone by nucleophilic aromatic substitution polycondensation. The polycondensations proceeded quantitatively in a N-methyl-2-pyrrolidone-toluene solvent system in the presence of anhydrous potassium carbonate to afford the polymers with inherent viscosities between 0.86 and 1.55 dL/g. The methyl-substituted poly(ether sulfone)s and poly(ether ketone)s showed good solubility in common organic solvents such as chloroform, tetrahydrofuran, pyridine, m-cresol, and N,N-dimethylacetamide. The tetramethyl- and hexamethyl-substituted aromatic polyethers had higher glass transition temperatures than the corresponding unsubstituted polymers, and did not decompose below 350 degrees C in both air and nitrogen atmospheres. The films of the methyl-substituted poly(ether ketone)s became insoluble in chloroform by the irradiation of ultraviolet light, indicating the occurrence of photochemical crosslinking reactions.