A novel method making use of block copolymer self-assembly in nematic liquid crystals (LCs) is described for preparing macroscopically oriented nanofibrils of p-conjugated semiconducting polymers. Upon cooling, a diblock copolymer composed of regioregular poly(3-hexylthiophene) (P3HT) and a liquid crystalline polymer (LCP) in a block-selective LC solvent can self-assemble into oriented nanofibrils exhibiting highly anisotropic absorption and polarized photoluminescence emission. An unusual feature of the nanofibrils is that P3HT chains are oriented along the fibrils' long axis. This general method makes it possible to use LCs as an anisotropic medium to grow oriented nanofibrils of many semiconducting polymers insoluble in LCs.