The study describes a design of experiment analysis performed on hybrid polymeric composites reinforced with unidirectional banana fibres and silica microparticles. Maleic anhydride was also evaluated as a chemical additive to improve the adhesion between phases. A full factorial design (2²3¹) and the analyses of variance were performed to identify the significance of the microstructure constituents against different mechanical and physical properties in a total population of 120 biocomposites samples. The microstructure parameters considered were fibre volume fraction (30% and 50%), silica addition (0%, 20 wt% and 33 wt%) and maleic anhydride addition (0% and 2 wt%). The mechanical and physical properties of the composite considered as factorial and analyses of variance responses were the apparent density, apparent porosity, water absorption, modulus of elasticity and mechanical strength under tensile and flexural loading. The design of experiment analysis has shown that the volume fraction of the fibres significantly affects all responses, with the composite made from 30% of banana fibres exhibiting superior mechanical strength and modulus of elasticity. While the addition of silica has featured a statistically noticeable contribution to the porosity and the water absorption, the presence of the particles did not provide any significant enhancement to the composites mechanical strength. Maleic anhydride showed a significant contribution to the apparent density, water absorption and flexural modulus, not improving the adhesion between phases, with a consequent decrease of the Young’s modulus and increase of the water absorption within the composites.