Composites are produced when two or more materials are used to give combination of properties that cannot be attained otherwise. This study aims to use crab shell and charcoal reinforcements to enhance the mechanical properties of polyester composites and decrease the environmental pollution caused by the agro waste. In this study, 5 – 25 wt. % of 100 g of grounded charcoal and crab shell with an average particles size of 150 µm were used for polyester matrix composites. Flexural strength, impact resistance, hardness and elastic modulus tests were carried out on the developed samples. The microstructure of the samples revealed a uniform distribution of the reinforcements within the polymer matrix with different morphology of the biocomposites. The results showed that the greatest flexural strength value of 361.37 MPa was obtained at 25 wt. % and the highest Brinell hardness number (BHN) was 118.27 at 20 wt. %. However, the highest modulus of elasticity was 335.63 MPa at 15 wt. % reinforcement with crab shell reinforced and was 308.64 MPa with charcoal reinforcements at 20 wt. %. Furthermore, the highest impact energy was 5.49 J for crab shell and 5.31 J for charcoal reinforced polyester composite. The development of the biocomposites of these materials will decrease the environmental pollution and improve the properties of the polyester matrix composites for engineering applications.