The Zanthoxylum bungeanum seed oil (ZSO) having high free fatty acids was successfully transformed into biodiesel by add-catalyzed esterification and alkali-catalyzed transesterification and high conversion to biodiesel was obtained in a short time compared to acid-catalyzed transesterification. Methanol-to-oil molar ratio, catalyst amount, and reaction time were found to clearly affect the ferric sulfate-catalyzed esterification of ZSO. The acid value of ZSO was reduced to less than 2 mg of KOH/g with a methanol-to-oil molar ratio of 16:1, catalyst amount of 2%, and reaction time of 3 h, following transesterification using an alkaline catalyst. The conversion to biodiesel by potassium hydroxide-catalyzed transesterification was achieved above 98% under optimum conditions: a methanol-to-oil molar ratio of 6:1, catalyst amount of 1.5%, reaction time of 60 min, and reaction temperature of 60 degrees C. The biodiesel production process was also confirmed by H-1 NMR and FTIR.