Highways are the most common and the most advanced means of transport compared to other transportation systems in Turkey. The embankment, subbase, base and pavement materials are provided from borrowed pits in traditional construction. During construction process; excavation, loading and transportation costs of the material are the most important factors for the total cost. In this research, the engineering properties of the soil are improved by mixing the soil with Class C fly ash and Virgin Homopolymer Polypropylene (VHP) using different combinations of them in order to avoid excess costs in the field construction. This paper represents the result of a study aimed at using mentioned alternative materials for stabilization of low plasticity clay subgrade of Sile district of Istanbul, Turkey. Various soil, fly ash and VHP mixtures were prepared in the laboratory and the engineering properties of these mixtures were observed. The unconfined compressive strengths of the mixtures were compared in order to estimate the optimum mix design of the stabilized soil. As a result, these improvement techniques were evaluated for the regular relevant standards of Turkey. It is expected that, the soil stabilization with these alternative materials provide the economic benefits and significant reduction of environmental pollution.