Rice husk ash, used as received (RHA) or milled (MHA), was investigated in natural rubber (NR) for its potential as a new type of filler. The physical testing of the NR vulcanizates involved tensile, tear, and abrasion resistance, hardness and resilience. The interaction between rice husk ash and natural rubber was investigated by swelling in an organic solvent. The effect of the coupling agent, bis(3-triethoxy-silylpropyl)-tetrasulfane (Si-69), on the curing and physical properties of the vulcanizates was investigated. The presence of the silane coupling agent has not brought the expected increase in properties, yet MHA exhibits the best overall vulcanizates properties when compared to RHA, although still inferior to commercial fillers as precipitated silica (Zeosil-175) and carbon black (N762), especially with regard to tensile strength and abrasion resistance.