A kind of polymer tube with (elliptical) ring structure is proposed for Terahertz (THz) guiding. The THz polymer tube has the low-loss property due to the fact that the central air core of the polymer tubes traps a large part of the mode power. Properties such as the effective index and the relative absorption loss of the THz polymer tube are investigated. The elliptical polymer tube with a cross-section of elliptical ring structure can be used as a highly birefringent low-loss THz waveguide with a high birefringence (up to the order of 0.01). The birefringence property of the elliptical polymer tubes with different parameters is also calculated and discussed.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.