Poly(ethylene glycol) (PEG) was modified with aniline groups at both the end, and then PEG-PANI rod-coil block polymers have been synthesized by polymerization of the aniline with the aniline-modified PEG. FTIR, NMR, and elemental analysis provided the chemical strucutre of the as-prepared polymers. The achiral rod-coil copolymer could form different superstructures by means of self-assembly when adding diethyl ether into its THF solution and the length of PANI segments is a key factor to the superstructures. AFM measurements revealed that they form spring-like helical superstructures from the short PANI-containing copolymers while these form fibrous helical superstructures from the longer PANI-containing copolymer. A possible mechanism of the helical superstructures is suggested in this article and the driving force is believed the pi-pi stacking of the rigid segment of the copolymers. (c) 2007 Wiley Periodicals, Inc.