Bioplastic films prepared from cornstarch incorporated with lemongrass essential oil (LEO) were evaluated in terms of their physicochemical and antibacterial properties. The films were prepared via solution casting to contain different amounts of LEO (0%, 0.5%, 1%, and 2% w/w). The films were characterized for thickness, color properties, moisture content, tensile strength, and elongation at break. Antibacterial activity against Staphylococcus aureus (BIOTECH 1582) and Salmonella typhimurium (BIOTECH 1826) was determined via disk diffusion using 6 mm film discs on Mueller–Hinton agar. Significant improvement in elongation at break (25.06 ± 7.39%) at 0.5% LEO, and increase in film thickness and moisture content with LEO addition were observed. All films containing LEO displayed strong antibacterial activity. Interestingly, the control film (0% LEO) exhibited notable baseline antibacterial activity (inhibition zones >29 mm) probably due to the vinegar and glycerol in its formulation. Considerable increase in antimicrobial activity occurs with 2% LEO against S. aureus. Overall, films prepared with 0.5% LEO showed the best possible balance between mechanical flexibility and antimicrobial activity, suggesting that this formulation may be used in preparing active food packaging materials.