Hemp fibre-reinforced polyester composites were prepared using a Resin Transfer Moulding (RTM) technique and the flexural and impact behaviour investigated. Flexural stress at break and flexural modulus showed an increasing trend with fibre content. Impact strength was found to decrease at low fibre content, then gradually increase with further addition of fibres. A strong interfacial adhesion between hemp and polyester was obtained using chemically modified hemp. This modification consisted in introducing reactive vinylic groups at the surface of the fibres, via esterification of hemp hydroxyl groups, using methacrylic anhydride. Increased bonding between fibres and matrix did not affect the flexural stress at break of the composite but was detrimental to toughness. This behaviour was ascribed to a change in the mode of failure, from fibre pull-out to fibre fracture, resulting in a marked reduction in the energy involved in the failure of the composite, leading to a more brittle material.