This paper describes the tensile and impact behaviour of polyester composites reinforced with continuous unidirectional sunhemp fibres of plant origin. The tensile strength and Young's modulus of sunhemp fibre were found to be 389 MPa and 35.4 GPa, respectively. Tensile strength of composites containing up to 0.4 fibre volume fraction (V_f) were found to increase linearly with (V_f) and the results showed good agreement with the rule of mixtures. The work of fracture, as determined by Izod impact test, was also found to increase linearly with (V_f) and the work of fracture for 0.24 (V_f) composite was found to be approximately 21 kJ m^-2. The analysis of various energy absorbing mechanisms during impact fracture showed that fibre pull out and interface fracture were the major contributions towards the high toughness of these composites. The results of this study indicate that sunhemp fibres have potential as reinforcing fillers in plastics in order to produce inexpensive materials with a high toughness.