The oxidative copolymerization of aniline and anilines derivatized at the 3-position with three different lengths of poly(ethyleneoxy) carboxylate groups was performed. The electric conductivities of the copolymers, measured by the four-point probe method, decreased as the content of aniline derivatives or the graft degree of bulky substituents in the copolymers increased. The more prominent conductivity drop was observed for the copolymer with the longer substituent at a given graft degree. Moreover, an increase in the graft degree of the copolymer induced a blue shift of the absorption bands in the near-IR region and significant line broadening of electron spin resonance signals together with a reduction in spin density. The X-ray diffraction patterns of the copolymer gradually lost the characteristic diffraction peaks of emeraldine hydrochloride as the graft degree of poly(ethylene oxide) (PEO) was increased. The changes in electric and spectroscopic characteristics with the use of PEO side chains on polyaniline backbones were attributed to the steric effects of the substituted poly(ethyleneoxy) carboxylate groups.