Expansive soil as a subgrade layer does not have sufficient geotechnical properties to construct buildings or roadways above it. To rectify the inadequacy in geotechnical parameters of expansive soil agro-waste soil stabilization was used in this study. Agro-waste soil stabilization is one of the eco-friendly and cost-control methods in soil stabilization. Palm Oil Fuel Ash (POFA) is one of the abundantly produced agro-waste from Palm oil factories. This study carries out the feasible uses of POFA by examining the compaction characteristics, unconfined compression strength (UCS), California bearing ratio (CBR), and Free swell index of the milled POFA-treated soil by adding 5, 10, 15, and 20% POFA to the soil. The milling process of the POFA was executed by the mechanical type of ball milling and to confirm particle size reduction particle size analysis and Blaine finesse test was carried out. The unconfined compression strength (UCS) properties of Raw POFA and milled POFA are compared to signify the efficiency of pulverization, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray microanalysis analysis (EDS) were carried out on POFA treated and virgin soil to examine the micro-structural changes. It is concluded from the current study that the milled POFA could be used for the stabilization of expansive soil highway subgrade and sub-base preparation.