The existing triacetylglycerol (TAG) production method involves esterification of oil (fat)-derived glycerol with acetic acid, forming a mixture of mono-, di- and tri- acetylglycerols. Herein, a new acyl exchange reaction is developed to directly and efficiently produce TAG from waste oils and fats by the driving effect of substituent size changes. Small-sized acetic acids easily replace large long-chain fatty acids of oils. This release in the intramolecular tension and diminishing of steric hindrance make TAG both thermodynamically and dynamically the most favorable product. Pure TAG was obtained with a high yield of 94.9%.