Large electrooptic effects based on the reorientation of liquid crystal molecules are expected in the high frequency electromagnetic wave region. However, there is only limited information about the optical and/or dielectric properties of the liquid crystal (LC) materials except for the visible and very low frequency region. Here, we try to determine the loss parameter and refractive index anisotropy of the commercially available nematic liquid crystal materials in the millimeter wave (MMW) region by using a V-band (50 Ghz - 75 GHz) rectangular waveguide test cell. Loss parameters are determined by fitting the theoretical data based on the multiple reflection phenomena to the measured transmission spectra. Refractive index anisotropy is derived from the phase difference between the horizontal and the vertical LC molecular orientation states. It is found that the usual nematic LC materials are transparent in the millimeter wave region and the refractive index anisotropy is still large.