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Abstract. To investigate a potential of terahertz spectroscopy to monitor starch degradation and biosynthesis in plants, we measured terahertz spectra (1.5-13.5 THz) of mung bean seedlings 2-8 days after germination and developing mung bean seeds 5-25 days after flowering, and compared to that of standard starch. Day 2 seedlings had 4 peaks at 9.1, 10.5, 12.2 and 13.1 THz, and their spectral features were consistent with standard starch. In addition, the peaks gradually disappeared in the subsequent 6 day growth period. On the other hand, in seeds, 4 peaks at 9.1, 10.5, 12.2 and 13.1 THz gradually appeared during 25 days of cultivation. These results suggest that the 4 peaks observed in mung bean plants originate from starch. To further investigate assignment of these 4 peaks, day 2 seedlings and seeds at 25 days were hydrolyzed by α-amylase, and terahertz spectra once again measured in a similar manner. Both seedlings and seeds showed that the peaks at 9.1 and 10.5 THz were not observed after being hydrolyzed, but the peaks at 12.2 and 13.1 THz remained after amylase hydrolysis. From these results, the peaks at 9.1 and 10.5 THz are sensitive to starch changes and useful indicators to monitor starch changes in mung bean plants. Additionally, the peak at 9.1 and 10.5 THz were correlated with starch content as quantified by chemical analysis. Our data demonstrated the potential of terahertz technology to monitor and quantify starch during degradation and biosynthesis processes in mung bean plants.