The functions of the chemicals are closely related with their compositions and structures. In this paper, we report the characterization of different lignin in the midribs of tobacco leaves using terahertz (THz) time-domain spectroscopy in the frequency range of 0.3 to 2 THz. These lignins are extracted from tobacco leaves grown in different regions. Lignin in midribs of tobacco leaves from the south region and the north region show distinctively different refractive indexes and absorption coefficients at THz frequency. The differences at THz range are found to be correlated with their chemical compositions, which are obtained by way of X-ray microanalysis. This clearly verifies that it is possible to employ THz time-domain spectroscopy as a tool for identifying the functions of the chemicals and analyzing their chemical compositions.