Guided-wave propagation of sub-ps terahertz (THz) pulses in a highly birefringent plastic photonic crystal fiber was studied by using a THz time domain spectroscopy technique. The plastic photonic crystal fiber was fabricated by using high density polyethylene tubes and solid filaments. The fabricated THz plastic photonic crystal fibers exhibit an extremely large birefringence of ~ 2.1 x 10(-2), which is almost one order of magnitude larger than that of previously reported photonic crystal fibers.