In this study, electrospun microfibers (MFs) were produced and used as key materials to optimize the composite with liquid crystal (LC) for terahertz (THz) wave phase shifters. These MFs, with an average diameter of 1.4 μm, were produced using the polymer solution concentration of 14 wt% and spinning voltage of 13 kV. When MFs were combined with LC, the measured results of the electrical characteristics showed that 14 wt% MFs provided an outstanding solution to the problem of a significant reduction in the natural birefringence of pure LC. The birefringence in the THz frequency range of the composite using 14 wt% MFs approached 90% compared with that using pure LC. Additionally, the decay time drastically shortened from hundreds of seconds for pure LC to hundreds of milliseconds for MF/LC composite and was independent of device thickness.