We report the crystalline behavior of poly(3-dodecylthiophene) (P3DDT) in aged toluene solution and link structure differences with the nature of seed nuclei related to various dissolution way. By directly stirring the P3DDT toluene solution for dissolution, the surviving fragments served as seed nuclei and star-like nanofibers were formed upon aging. While by heating the P3DDT solution for complete dissolution followed by cooling, the seed nuclei came from the pi-pi stacking of the planarized P3DDT chains and linear nanofibers were formed upon aging. Formation mechanisms and kinetics of different nanofibers are discussed in detail. (C) 2013 Wiley Periodicals, Inc.