Interest in biodegradable polymers has been increasing exponentially due to the global environmental concerns about inappropriate disposal of plastic materials. Considering this issue, poly (butylene adipate-co-terephthalate) (PBAT) is a good candidate to be applied to films, since it presents desirable, promising processability and thermal-mechanical properties and lower water solubility compared with other biopolymers. However, PBAT exhibits inferior mechanical properties compared with polyolefins. To overcome this, acetylated cellulose nanocrystals (CNCs-Ac) were systematically investigated by incorporating different weight ratios to PBAT-based films produced via a solvent casting/heat pressing approach. This process combines a well dispersed hydrophobic filler with additional temperature and pressing, ensuring improvement in yield strength (30%) and Young’s modulus (90%), as well as an outstanding benefit in flexibility (> 650%), compared with neat PBAT film. This work provided a novel route to prepare PBAT bionanocomposites, showing greater potential for biodegradable packaging, which can be an alternative to conventional polymers.