Biodiesel (BD) is the product of catalysed transesterification reaction, in which fatty acid (FA) is transformed to fatty acid methyl ester (FAME), named BD. The frequency-dependent absorption and refractive characters of BDs and its base stocks have been researched in the spectral range of 0.2-1.5 THz by terahertz time-domain spectroscopy (THz-TDS). The BDs showed higher absorption value than those of its base stocks because of the concomitant, and the increasing of absorption coefficients of three BDs differed with the different transesterification technology. The results suggested that THz-TDS can be a promising method to the quality control and ester transfer efficiency analysis of BD.