Normally, U is present in most soils at very low concentrations. According to the United Nations, the normal concentration of U in soils is within the range of 0.3 - 11.7 mg kg-1. The U behavior in soils is very complicated, this because U can be associated with numerous compounds and phases and many factors affect its behavior in soil. Few investigations have been published assessing the U bioavailability and the factors affecting the U bioavailability in soils. Better understanding of different factors governing the U behavior in soils is very useful because it leads to the best possible extraction procedures and the best remediation treatments in U-affected soils.