Terahertz (THz) conductivity of single walled carbon nanotube (SWNT)/poly-vinyl alcohol (PVA) composites has been studied in the frequency window of 0.3-2.0 THz. It is found that conductivity of these samples can be efficiently tuned by changing the length of the SWNTs and also the SWNT weight fraction. For the highest weight fraction at a frequency of 1 THz, longer SWNT sample (average length ~15 μm) showed ~90% increased conductivity than its shorter counterpart (average length ~2 μm) having the same diameter. A modified Universal Dielectric Response (UDR) model is applied to analyze the conductivity spectra.