Generating large quantities of contaminated soil annually in all parts of the world poses a great threat to the environment and humans. In recent times there have been multiple sources of soil contamination. One of the most famous of these contaminants is the used engine oil. In this research, the effect of waste engine oilon some geotechnical properties of soil were studied. Laboratory tests including compaction and California bearing ratio (CBR tests were conducted on clean and contaminated soil. Contaminated soil samples were prepared by adding the waste engine oilat ratios of 4%, 8%, 12% and 16% of the dry weight of the samples. The results revealed a positive effect of the waste engine oilon the maximum dry density (MDD) and CBR values, but this improvement continued until the contaminant ratio of 8%. These values were decreased with further increase in the contaminant ratio to 16%.