As the exploration of higher frequencies extends into Millimeter-wave (mmW) band and beyond, the hollow rectangular waveguide (HRWG) emerges as an increasingly attractive interconnect option due to its low-loss air medium, isolated propagation environment, and high-power handling capability. However, the challenges of traditional fabrication methods become more pronounced with increasing frequencies, necessitating innovative and compact solutions. In this study, we proposed a novel waveguide technology based on vertically aligned carbon nanotubes (VACNTs), renowned for their exceptional mechanical and electrical properties. Our work utilizes a low-temperature CNT transfer technology, addressing limitations related to high CNT growth temperature and poor adhesion. Measurement results demonstrate promising waveguide performance across a flat bandwidth of almost an octave (60-110 GHz), with losses closely aligned with simulated curves. Experimental validation reveals the ability of VACNT waveguides to carry wideband digital modulated channels at 60 GHz, facilitated by the flat response of the VACNT. This research showcases the potential of VACNT-based waveguide structures as viable alternatives to conventional metallic waveguides, offering excellent transmission and flatness properties.