This paper investigates the use of vertically aligned carbon nanotube (VACNT) arrays as building blocks for mm-wave waveguide devices. The fabrication, characterization, and performance evaluation of VACNT-based waveguides are presented. The waveguides are fabricated using a low-temperature 3D packaging technology, and their transmission properties are assessed through S-parameter measurements. The results demonstrate the potentiality of the VACNT-based waveguide topologies within the mm-wave frequency range. Simulations are conducted to understand the loss mechanisms in VACNT-based waveguides and compared with experimental measurements. The low conductivity of the CNT array introduces additional loss compared to metal-based waveguides. Bonding misalignment is also found to impact the overall loss.