In roadway systems, fine grained soils which are characterized by high volume change potential, low dry density, and low engineering strength property are not preferable for subgrade, subbase/base course material. The regional soil in Southeast Idaho is characterized by silt bess which is notorious for instability due to sensitivity to moisture ground vibration. One method of improving the strength of such type of soil is lime-fly ash stabilization. The present study deals with the investigation of the beneficial effect of lime-fly ash treatment to subgrade pavement. The engineering properties and strength tests that were selected to evaluate the performance of both the treated and untreated soils were Atterberg limit, Proctor compaction, soil pH, Unconfined Compression (UCC), and California Bearing Ratio (CBR) tests. It was found that lime-fly ash treatment significantly improved the bearing strength of the soil. The lime-fly ash stabilized soil produced ultimate compaction, proper drainage, insignificant volumetric change and higher strength values.