In this study, we investigate the influence of silica colloids on the migration of radionuclides (U and Th) in the subsurface medium. Colloidal suspension of silica was generated from tetraethyl orthosilicate (TEOS) and spiked with U and Th in the concentration range of 10–100μg mL^-1. Concentration of U and Th recovered out of the experimental soil column in case of colloidal assisted migration was 84.5 and 16.1 % respectively whereas the same was 27.2 and 15.9 % for ionic solution. Mean linear attenuation coefficient as evaluated experimentally for colloidal assisted migration was 0.07 and 0.12 cm^-1 for U and Th respectively whereas the same in case of ionic solution was 0.13 and 0.17 cm^-1.