Acetylated monoglyceride (AMG) is one of the most innoxious and effective external plasticizers for poly (vinyl chloride) (PVC) food packaging film because it is approved as a food additive and its carbonyl group of a carboxylic ester and aliphatic side chain of an ester allow unique interactions with PVC. Monoglyceride moieties can vary because the alkyl chain length is mainly derived from fatty acids of vegetable oils, and AMG enhances the flexibility and elasticity of PVC polymers. To investigate the influence of alkyl chain length, the thermal properties and mechanical performance of AMGs consisting of caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid were studied in a PVC system. The optimum alkyl chain length for an AMG was C14:0, based on data obtained from stress at break, strain at break, Young’s modulus, glass transition temperature, thermal degradation, and migration rate tests.