Incorporation of rice husk ash (RHA) fillers into polypropylene affected some of the thermal properties of polypropylene composites. Addition of the black rice husk ash (BRHA) filler raised the thermal degradation temperature while maintaining the oxidative stability. The thermal degradation temperature of the white rice husk ash (WRHA) composites was found to be independent of filler loading but the oxidative stability deteriorated with increasing filler content. DSC studies indicated that both white and black RHA fillers act as weak nucleation agents and increase the degree of crystallinity of polypropylene by a small margin. Addition of the RHA fillers reduced the linear thermal expansion coefficient of the composites. Dynamic mechanical studies showed that the RHA composites with higher filler content have higher storage modulus. Tan δ curves of the composites indicated that WRHA filler increased the damping property while the BRHA filler had an opposite effect.