This thesis investigates the impact of biomass-based diesel (including biodiesel and renewable die-sel) on soybean prices. The study begins by exploring the economics of biomass-based diesel, elu-cidating factors influencing its pricing, its interconnections with other products in the fuel market, and the economic ramifications of biofuel policies on the biomass-based diesel industry. Subse-quently, a theoretical linkage between biodiesel and soybean oil prices is established, and the pivot-al role of soybean oil in determining soybean prices is shown empirically. This framework lays the groundwork for understanding how biomass-based diesel influences soybean prices. Then I con-struct a theoretical model to show that the soybean price increase resulting from the biomass-based diesel shock can be moderated due to the increase in soybean production and decrease in soybean meal prices. Lastly, a simulation model is constructed to quantify the short run and long run impact of biomass-based diesel on soybean prices. The analysis reveals that increases in biomass-based diesel production and prices significantly contribute to soybean price surges observed in 2007-2008, 2010-2012, and 2020-2022. Furthermore, the emergence of renewable diesel, particu-larly prominent from 2021 onwards, profoundly affects the profitability of biodiesel and exerts a substantial influence on soybean prices.