The ever-increasing demand for substitute energy sources encourages the usage of biofuels as transportation fuel; however, the unstable properties and low calorific value of biofuels caused by high oxygen content limits their direct application. In this study, we report the upgrading of a model biofuel in octanoic acid by hydrodeoxygenation (HDO) using RuSn supported on SiO2-doped Al2O3 (SiAl). The presence of SiO2 on Al2O3 was crucial for the formation of Ru3Sn7 alloy phase because SiO2 modified the metal-support interaction between RuSn and Al2O3. The alloy phase conferred significant hydrogenation activity to convert octanoic acid to octanol and minimized carbon loss by reducing decarbonylation activity. The deposition of SiO2 also resulted in improved acidity, which increased with increasing SiO2 loading from 10 to 30 %, due to the formation of isolated terminal silanols (Si-OH). The presence of the silanol groups was important for dehydration of octanol to octane, since the silanols retained octenes longer on the support, facilitating over-hydrogenation. The cooperative metal-support activity on RuSn/SiAl enables high and selective hydrogenation and dehydration activity for upgrading fatty acids in biofuel to hydrocarbons.