Composite films that utilize seaweed as a matrix and oil palm shell (OPS) nanoparticles as a reinforcing material were developed. The effects of loading OPS nanoparticle (0%, 1%, 5%, 10%, 20%, and 30%) into seaweed films were determined by analyzing the physical, mechanical, and morphological properties of the films. The seaweed-based film incorporated with OPS nanoparticles at a high concentration (20% w/w) achieved the highest tensile strength (44.8 MPa) and Young’s Modulus (3.13 GPa). However, the film’s hydrophobicity (contact angle = 47.3º) and percentage of elongation at break (2.10%) were reduced. Moreover, it was observed that excessive loading of nanofillers (> 20%) reduced the tensile strength and hydrophilicity of the film. This phenomenon was attributed to the agglomeration of OPS nanoparticles and the formation of large voids on the film surface. Thus, the relative effectiveness of the various tested nanofiller contents in enhancing the mechanical strength of the composite film were found to be ranked in the following order: 20%, 10%, 5%, 30%, and 1%.