Carbon-rich substances found in both natural and artificial habitats on land and water are referred to as organic matter. It is composed of organic constituents derived from the waste and remains of living things, including plants and animals. Due to its complex and dualistic behavior, organic matter plays an important role in the solubility of uranium in environmental systems, acting as both a friend and a foe to the solubility of uranium depending upon the conditions. By forming stable soluble complexes with uranium ions, organic matter can enhance uranium mobility, thus increasing uranium solubility in aqueous environments. The precipitation of uranium is prevented by generating compounds with humic and fulvic acids, which may be transported through groundwater systems more readily. Organic materials can play a key role in reducing uranium(VI) to uranium(IV), which tends to precipitate as uraninite, which is less soluble, resulting in a lower solubility of uranium. The dual effects of organic matter are affected by pH, redox conditions, the type and concentration of organic matter, and competing ions. To develop effective uranium remediation strategies and predict uranium mobility in natural and contaminated environments, it is essential to consider the specific interactions between organic materials and uranium. The complex relationship between organic matter and uranium solubility and the significance for environmental management and remediation effects are illustrated in this chapter.