The dielectric properties of skin tissue phantoms with glycerin concentrations from 0% to 60% were investigated in a terahertz region. Their complex relative permittivities were measured by the terahertz time-domain spectrometer between 0.1 THz and 0.8 THz. The complex relative permittivities decreased with the increase of the glycerin concentration. On the basis of the property it was found out that the permittivities of the phantom with 35% glycerin was close to that of skin.