Terahertz (THz) spectra of two TNT-related compounds (4-NT and 2,6-DNT) are investigated using Fourier transform infrared spectroscopy (FTIR) and THz time-domain spectroscopy (THz-TDS) between 0.1 to 20 THz. The Density Functional Theory (DFT) is applied to calculate the THz spectra of these two compounds. The transmission, diffuse reflection, and calculated spectra are in good agreement. The measured THz resonance lines from the transmission and diffuse reflectance spectra are assigned based on DFT simulation. The observed THz signatures imply that the THz spectrum has potential for standoff detection of explosive and related compounds (ERCs) in the THz range.