Recently, the glut of residues generated from the oil palm mill sector has become a topical global issue due to poor management strategies that constitute environmental risks. This work focused on the characterization of palm oil mill ashes to improve the bearing strength of weak soil. Palm oil mill ashes, namely boiler bottom ash (POMBBA), boiler retained fly ash (POMBFA), and collector fly ash (POMFA) from the incineration process of oil palm biomass were characterized. The morphology of palm oil mill ashes was observed under scanning electron microscopy (SEM). Scanning electron microscope-energy dispersive X-ray analysis was used to analyze the chemical and physical properties of the ashes, with mineral coal fly ash as a control in comparison to palm oil mill ashes. Results of the chemical composition of coal fly ash (CoFA) revealed that it was rich in silicon dioxide (SiO2) with over 38.55%, POMBBA 39.53%, POMBFA 34.77%, and POMFA 15.08% respectively. Yet, enhancement of soft soil requires the presence of Al2O3, Fe2O3, and CaO, to produce a composite with adequate strength. All the chemical constituents of the studied ashes exhibit pozzolanic and cementitious properties, which could reinforce soil bearing capacity and a low-cost binder in the road construction sector.