Hierarchical poly(3-hexylthiophene)(P3HT)/carbon nanotube (CNT) supramolecular structures were fabricated through a bottom-up CNT induced P3HT crystallization strategy. P3HT nanowires growing perpendicular from CNT surface have uniform width and height. The density and the length of these nanowires can be controlled by tuning the P3HT/CNT mass ratio. The quasi-isothermal crystallization process monitored by in situ UV-Vis spectroscopy indicates that CNTs can greatly enhance the P3HT crystallization, and the P3HT nanowire formation follows first-order kinetics. Such bottom-up strategy provides a general approach to build 2D functional conductive supramolecular structures that will lead to numerous applications in nanoscale electronics.