Metallic rod array is successfully demonstrated to be integrated a parallel plate waveguide and used as a slab-waveguide for sensing applications. Both the waveguide properties are characterized from the transmission spectra using different polarization conditions of terahertz electromagnetic fields, which are parallel and perpendicular to the rod axis. When THz field polarization is parallel to the rod axis, there is high-pass filtering feature with structure-period-dependent threshold frequency, corresponding to the plasma frequency of the rod-array composite. For the polarization perpendicular to the rod axis, there is Bragg diffraction frequency as forbidden band with considerably low transmission power. The metal-rod-array integrated parallel-plate waveguide is connected with a microfluidic channel to sense liquids, and the minimum detectable quantity is about 13μmol/mm3. The metal-rod-array slab waveguide is able to sense thinfilm with nanometer level, and the detectable optical path difference is down to λ/2380. The sensor properties of multiple functions for sensing various analyte conformations, microfluidic integration and high sensitivity would be applied in biomedicine and biochemical applications.