AbstractThis research aims to study the effects of degradation on mechanical, physical, and morphological properties of empty fruit bunch (EFB) fiber- reinforced polyester composites. The unsaturated polyester resin has been used to produce thermoset polymer composites. The reinforcing effect in composites was evaluated at various fiber loadings, including an overall fiber content (by weight) of 20% and 40%. The mechanical (tensile, flexural, and impact) and physical (density, moisture content, and water absorption) properties were studied before and after the samples were buried in the soil for period of 12 months. Scanning electron microscope (SEM) analysis was conducted to visualize the effect of the quality of adhesion between the fibers and matrix. The soil burial investigation results revealed that EFB fiber-polyester composites showed highest degradation percentage as compared to polyester resin and fiberglass.