Modified copolyether sulfones with bulky azo pendant groups were synthesized by a polycondensation reaction of some polysulfones containing aldehyde groups with p-aminoazobenzene. The corresponding model compound and an azo oligomer were also prepared to compare their properties. The structure of the resulting compounds was confirmed by IR, H-1-NMR spectra, and elemental analyses. The polymers were characterized by reduced viscosity, thermogravimetric analysis, and differential scanning calorimetry. The photochemical behavior of the azoaromatic chromophores was followed by UV-visible absorption spectroscopy. Two kinds of photoreactions (photoisomerization and photodecoloration) operate in these polymers.