In the nature, CO2 and water are converted into biomass or organics via photosynthesis and geochemistry, respectively. The use of renewable biomass for CO2 reduction under hydrothermal conditions means the integration of photosynthesis and geochemistry for CO2 reduction, and then a rapid and highly efficient CO2 reduction can be expected. Here, we report a hydrothermal reduction of CO2/NaHCO3 by using biomass-derivative hexanehexol, which has the most similar structure to carbohydrate biomass, as a preliminary work for CO2 reduction with real biomass. We show that NaHCO3 can be reduced into formate, and an about 80% yield of formate based on the initial hexanehexol was achieved at 300 degrees C for 1 h.