The effects of Caulerpa lentillifera (CL) extract incorporation on antioxidant activity, antibacterial activity, water stability, and physical properties of the chitosan/gelatin (CS/GEL) films were studied. The CL extract containing CS/GEL composite film was prepared by the casting method. The effect of CL content (1%, 3%, 5%) on the antioxidant properties, thermal property, mechanical properties, barrier properties, water stability and water contact angle of CS/GEL films was evaluated. With the increase of CL extract content, bumps and micro-pores appeared on the surface and cross-section of the composite films. The water contact angle, water solubility, and water absorption swelling rate of the composite films were improved with the addition of CL; therefore, the composite films exhibited better water stability. The TS of films were enhanced (from 12.57 to 23.66 MPa). Compared with the normal CS/GEL films, the CS/ GEL-CL films exhibited better antioxidant with DPPH scavenging capacity values of 72.6% and could effectively slow down the lipid oxidation of refrigerated pork samples during storage, such as lower accumulation of free fatty acid content and fluorescence compound formation. This suggested that CS/GEL-CL film might be suitable as active films for food packaging.