Biobased lipoic acid (LA) can be used as a plasticizer and combine with ethyl cellulose (EC) to form ethyl cellulose supramolecular composite films. The morphology, hydrophilic performance, thermal stability and mechanical properties of the composite films were investigated. The introduction of LA can significantly improve the flexibility and processability of ethyl cellulose films because LA can weaken both hydrogen bonding and hydrophobic interaction in EC chains. The elongation at break of EC composite films can be increased by 5.5~11.1 times when the LA content is 20~50%. In addition, comparative experiments and molecular dynamic simulations were performed to explain the superiority of LA as a plasticizer for EC films. Graphic abstract