In this work, the effort is directed to assess the feasibility of immobilizing the ash produced from the incineration of solid radioactive wastes. Within this context, the ash was characterized to determine its chemical composition and physical properties. Immobilized cement-ash matrices have been prepared to investigate the influence of waste to cement ratio. To characterize the extent of the solidification process of the immobilized waste matrices, the mechanical strength test was conducted. The standard mass transfer leach test has been employed to test the extent of Cs-137 and Co-60 stabilization. Non-linear fitting of the experimental leach data to different mathematical models was conducted to evaluate the mechanisms those instigate the leaching phenomena and the leaching parameters were determined. The controlling leaching mechanism and leachability indices were calculated for the studied waste matrices. The results indicated that Cs-137 leaching is resulted from first-order reaction between the surface of the waste matrix and the leaching solution followed by diffusion through the studied matrices. The leaching of (60)This research has been conducted within the corporation research project (CRP) "Modeling the long-term leaching behavior of some radionuclides commonly encountered in low and intermediate level radioactive wastes from different stabilized waste matrices" As a part of the IAEA CRP "Behaviors of Cementatious Materials in Long Term Storage and Disposal".Co was found to be as result of four subsequent mechanisms that include release of loosely bound Co-60 followed by first-order reaction the diffusion and finally dissolution. It was found that the studied immobilized waste matrices have acceptable mechanical performance. The values of the leachability indices indicate that the performance of the studied matrices in Cs-137 stabilization is not acceptable. (C) 2009 Elsevier B. V. All rights reserved.