Abstract: The spectral properties of various fabrics were investigated by using terahertz time-domain spectroscopy. Through measuring the time-domain spectra in experiments and calculating frequency-domain spectra by applying the fast Fourier-transform (FFT) to each pulse waveform, the spectral information of fabrics in terahertz region, especially the transmission and absorbance, was obtained and analyzed. It is well demonstrated that the fabrics, which are opaque in visible light, are almost transparent in terahertz region and no special absorption spectra. This research has a great influence on identifying the concealed danger and terahertz imaging.