The absorption spectra and refractive index of 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2,6-DNT) were measured in the region of 0.3-2.0 THz by terahertz time-domain spectroscopy (THz-TDS) at room temperature. Gaussian 03 program was applied to predict geometric structure and vibrational frequencies of 2,6-DNT. Three absorption peaks at 1.09, 1.36 and 1.55 THz of 2,6-DNT were obtained and assigned to intermolecular interactions. Quantitative analysis with THz-TDS was undertaken for the mixture of 2,4-DNT and 2,6-DNT. The analytic weight ratio of 2,4-DNT to 2,6-DNT is consistent with the actual one with an analytic error of about 8%.