Biodegradable edible films are increasingly used to extend food shelf life while reducing dependence on synthetic plastics. Casein, a milk protein, exhibits excellent film-forming characteristics, and its performance can be improved by incorporating plant-based antioxidants. Basil (O. basilicum) leaves are known to contain phenolic and flavonoid compounds with strong antioxidant potential. This study investigated how varying levels of basil leaf extract (5%, 6%, and 7%) influence the antioxidant and physical properties of casein-based edible films. Film-forming solutions were prepared from 3% (w/v) casein and 1.5% (w/v) konjac flour, heated at 80 °C for 30 minutes, poured into molds, and dried at 50 °C for eight hours. Antioxidant activity was assessed using the DPPH radical scavenging method at 515 nm, while film thickness, gelation time, and dissolution time were measured using standard procedures. The results revealed that increasing basil extract concentration enhanced both the thickness and antioxidant activity of the films. At 7% extract, film thickness reached 0.133 mm, antioxidant activity increased to 17.93%, and gelation and dissolution times decreased to 10.65 sec and 6.50 min, respectively. These outcomes indicate that basil leaf extract improves the functional and physical qualities of casein-based edible films. The findings highlight the potential of basil as a natural additive for developing active, eco-friendly food packaging materials.