Summary form only given. We believe we report the first demonstration of waveguide propagation of sub-ps THz pulses in a dielectric fiber. The experimental arrangement employed for coupling of free-space single-cycle THz radiation to the fiber is similar to that used for investigations of THz propagation in metallic waveguides. Briefly, the THz radiation is focused by a silicon lens to a waist diameter of /spl ap/200 /spl mu/m with the fiber entrance face placed at the waist position. An identical arrangement is used at the exit face of the sapphire fiber.