Multiwalled carbon nanotube (MWCNT) thin films deposited on fused quartz substrates are characterized by continuous wave subterahertz free space technique using a vector network analyzer (VNA). The scattering (S) parameters are measured by a VNA in the frequency range of 220-325 GHz (G-band) and 325-500 GHz (Y-band). The complex refractive index is extracted with the help of Nicholson-Ross-Weir method. The transmission and absorption of the thin films are also studied. VNA offers a good spectral resolution and a dynamic range of 60-70 dB around 500 GHz. The experimental technique and material parameter extraction procedures are described. The refractive index, transmission and absorption coefficient obtained for MWCNT thin films are plotted and the results are discussed. © 2014 Wiley Periodicals, Inc.