Abstract: The principle of tomographic gamma scanning (TGS) method for nondestructive assay of heterogeneous radioactive waste was described. An experiment of a 200 liter drum detection was conducted using the radioisotope 152Eu as the transmission source. A polar voxel representation was used, and the efficiency matrix was calculated by MCNP codes. The algebraic reconstruction technique and maximum likelihood expectationmaximization method were adopted for transmission and emission reconstruction to get the distribution of linear attenuation coefficient and radioactivity, respectively. The TGS results are obviously　better than segmented gamma scanning (SGS) results, fitting the real activity very well with a relative error less than 10%. The results indicate that the polar voxel representation and reconstruction algorithms are feasible.