Abstract: The absorption spectra of folic acid and retinoic acid were measured in 0.2-1.8 THz using terahertz time-domain spectroscopy (THz-TDS) system at room temperature, and the refractive index was obtained as well. Experimental results indicate that folic acid and retinoic acid both have distinct absorption features in the THz region, which can be used as fingerprints for the molecular recognition. At the same time, the Gaussian03 was used for isolated-molecule simulation, the density function B3LYP and Gaussian-type basis set 6-31 G(d,p) were chosen to perform all the theoretical simulations. Experimental results were in good agreement with the simulation. Meanwhile, the vibration modes for different absorption peaks of folic acid and retinoic acid were recognized by using Gaussian-View3.0. This work could be as certain references in kind of vitamin molecules recognition and new medicine research.