In the present study, characterization and morphological study of oil palm ash (OPA) and thermal properties of OPA-filled natural rubber (NR) compounds were carried out. The morphological study revealed that the OPA particle was irregular with rough surface and porous structure. Energy dispersive x-ray analysis and an x-ray fluorescence spectrometry indicated that silicon was the highest component in OPA. Fourier transform infrared analysis and x-ray diffraction indicated that the main mineralogical components in OPA were quartz and calcite. The study results of the OPA-filled NR compounds showed that the thermal resistance and retention properties after thermal ageing were notably enhanced with the addition of OPA and improved as the OPA loading was increased.