Fatty nitriles are widely used as intermediate molecules in the pharmaceutical and polymer industries. In addition, hydrogenation of fatty nitriles produces fatty amines that are common surfactants. In the conventional fatty nitrile process, triglycerides are first hydrolyzed and the resulting fatty acids are catalytically reacted with NH3 in a liquid-phase reaction. In this study, we report a simpler one-step fatty nitrile production method that involves a direct vapor-phase reaction of triglycerides with NH3 in the presence of heterogeneous solid acid catalysts. The reactions were performed in a tubular reactor maintained at 400 °C into which triglycerides were injected through an atomizer to allow rapid volatilization and reaction; NH3 was fed as a gas. Several metal oxide catalysts were tested, and reactions in the presence of V2O5 resulted in near-theoretical fatty nitrile yields (84 wt % relative to the feed mass). In general, catalysts with higher acidity such as V2O5, Fe2O3, and ZnO showed higher fatty nitrile yields compared to low acidity catalysts such as ZrO, Al2O3, and CuO. Energy balance calculations indicate that the one-step reaction described here would require significantly lower energy than the conventional process primarily because of the elimination of the energy-intense triglyceride hydrolysis.