Metal leaching from coal fly ashes into the environment is of a much concern. A series of batch tests were performed to investigate the potential leaching of metals from fly ash modified with organosilane (OS) and quaternary ammonium surfactant (SF). The fly ash was collected at the Figueira Thermal Power Plant, located in the city of Figueira, State of Paran??. Firstly, the influence of ash mass/water volume ratio on the concentration of the elements in the leachates from untreated fly ash was evaluated. Subsequently, the capacities of immobilization of toxic elements by the different immobilizing agents were determined by measuring the pH and conductivity of the leachates from the treated fly ash. A significant reduction in the concentration of the elements was observed for all the leachate samples obtained from the ashes treated with OS. The concentrations were reduced by 89%, 77%, 42% and 11% for Cr, Mo, As and Se, respectively. When SF was used for the ash treatment, the concentration reduction in the leachates was found to be above 60% for all elements. These results show that both the OS and SF can be used as immobilizing agents for the retention of toxic elements presented in coal ashes.