Assembling soft matters such as polymers into ordered structures remains as a challenge because of their intrinsic flexibility that can easily lead to entanglements and disordered bundles. This work demonstrates that macroscopic P3HT fibers (several cm) can be formed via DC electric field induced assembly of pre-aggregated high-aspect ratio P3HT nanowhiskers in solution. The P3HT fibers assemble along the local electric field directions including curved electric field lines. The impacts of DC electric field strength, solvent polarity, and nanowire microstructure types on the assembly process are studied, leading to a proposed assembly mechanism. This method provides a general way of electrokinetically assembling flexible molecules such as conjugated polymers by utilizing their secondary 1D nanoaggregates as the building blocks. The assembled macroscopic fibers remain high crystallinity and do not dissociate back into nanowires after the electric field is removed, offering intriguing opportunities for a variety of optoelectronic applications. (C) 2018 Elsevier Ltd. All rights reserved.