Abstract In this study, rice husk ash (RHA) and commercial silica were used as reinforcing fillers in natural rubber (NR). XRF, FTIR, SEM and particle size analysis were used to characterize RHA and commercial silica. Silica contents in RHA and commercial silica were 91.413% and 98.693%, respectively. Particle size of RHA was larger than that of commercial silica. Cure characteristics, mechanical properties and morphology of NR reinforced with RHA and commercial silica were compared. RHA/NR composite showed shorter scorch time and cure time when compared to silica/NR composite. Mechanical properties of commercial silica/NR composite were higher than those of RHA/NR composite. Silane coupling agent (Si69) increased mechanical properties but reduced scorch time and cure time of the NR composites. SEM results revealed that Si69 improved the compatibility between the filler and NR matrix.