Starch is a reasonably cheap, renewable and environmentally friendly resource. With a view to developing a new type of rubber composite based on starch, the objective of the study was to assess the factors affecting the reinforcing effect of starch and determine how reinforcement could be maximised In general, the study shows relatively poor reinforcement of natural rubber by starch, resulting in compounds of low stiffness and strength compared to compounds filled to a similar volume fraction with carbon black. The poor reinforcement is due to a weak interaction between polar starch and non-polar rubber and due to the large particle size of starch. However, the addition of polybutadiene maleic anhydride (PBMAH) and resorcinol formaldehyde (RF) coupling agents significantly improved the rubber to filler adhesion.