Contamination of soil and groundwater by organic and toxic substances is a common environmental problem. Crude oil and petroleum products are considered as one of the most important environmental pollutants. The most important concern about petroleum products is related to their harmful effects on health and also ecology of soil during all stages of refining, traortation and utilization. However, the issue of soil pollution caused by oil spills is geotechnically important. Due to the physico-chemical reactions occurring between pollutants and soil, the geotechnical behavior of soil is changed. This could cause reduction of bearing capacity of soil. But there are different methods to refine and control contamination of polluted soils. Among them, heating methods are one of the best techniques to sanitize organic compounds from soil. One way to provide the necessary energy to raise the temperature of the soil to break down hydrocarbons is use of microwaves. In this study, the geotechnical properties of soils contaminated with crude oil and stabilization of slag and nano-clay and also the state after decontaminating by micro waves are evaluated. The best efficiency of removal in the initial experiments with 10% moisture, 10% activated granule carbon and 1000 watt microwave power reached to 81 percent. In weight of 339 grams, i.e. the amount of soil needed to perform direct shear test, this removal efficiency was 78% due to device limitations. With direct shear tests on the soil with 4%pollution, cohesion and internal friction angle of soil were achieved 40 kPa and 5/29 degrees, respectively and for 8%Pollution a 33 kPa and 29 degrees, respectively. Cohesion and internal friction angle of contaminated soils (4 and 8%) after cleansing were evaluated; their values for both infections were achieved 52 kPa and 33 degrees, respectively. With the addition of 10% slag (optimum percentage of slag) to contaminated soil, cohesion and internal friction angle were achieved as 145 kPa of 50 degrees, respectively while adding 10% slag to refined soil increased the values of cohesion and internal friction angle to 213 kPa and 51 degrees, respectively. Also by adding 25/2 percentage of nanoclay (optimum percentage of nanoclay), adhesion and internal friction angle in the refined soil increased from 101 kPa and 42 degrees, respectively, to 180 kPa and 5/43 degrees, respectively. It was found that the angle of internal friction have not changed significantly after stabilized decontamination while adhesion increases 5/1 times for the established mode with slag and 8/1 times for the fixed mode with nano-clay. In general, performance of slag to nano-clay was better in terms of improvement of soil strength better before and after decontamination. Key Words: microwave, Contamination of soil by crude oil, cleaning, soil strenghth