This study reports the developmentBioplastic ofCharacterization starch-based biopolymerBiopolymers films using Sargassum spp. (1.3–10% w/w) and sawdust (8.5–13.6% w/w) as fillers, following a 2-factor, 4-level factorial design. The optimal formulation, with a 35:16 mass ratio of sawdust to sargassum, exhibited a density of 1.3 g/mL, a 3.5% moisture content, a 19.4% solubility, a 27.3% water absorption, and a 40% biodegradability. Mechanical testing indicated improved flexibility with moderate tensile strength. TGA confirmed thermal stability, while X-ray diffraction (XRDX-ray Diffraction (XRD)) analysis revealed semi-crystalline features attributed to cellulose and alginate structures. SEM–EDS revealed a heterogeneous but cohesive morphology. These findings suggest strong compatibility among the components and highlight the potential of this biopolymerBiopolymers for use in packaging and agricultural applications, contributing to biomass valorization and sustainable materials development within a circular economy framework.