With respect to the fact that highways are the most common and the most advanced means of transport compared to the other transportation systems in Turkey, alternative techniques and materials are constantly being investigated in order to develop innovative solutions for the construction of highway embankments and other types of earth structures. It is obvious that in highway projects, excavation, loading and transportation costs of the material are the most important factors for the total cost. Hence, improvement in subgrade soils would have significant economical side effects. In this research, laboratory experiments have been performed to investigate the use of polypropylene fibers in order to stabilize two different high and low plasticity clay soils. Various soil and polypropylene fiber mixtures were prepared in the laboratory and the engineering properties of these mixtures were observed. The compaction and CBR characteristics and the unconfined compressive strength of samples were investigated. This paper illustrates the findings from the laboratory researched with particular emphasis on the use of mentioned alternative materials that provide economic benefits as well as reduced environmental impacts. © 2013 American Society of Civil Engineers.