The structural details of a bifunctional Pt/USY catalyst were studied using electron tomography. As a part of a fundamental study on the synthesis of Pt/USY catalyst, H2PtCl6 precursor was used for the impregnation of USY zeolite support as a source of negatively charged PtCl62- ions in order to restrict interaction with acidic sites of USY zeolite. After heat treatments, it was visualized in 3D that some Pt particles were 3–4 nm in size, while the majority maintained the size of 1.2–1.5 nm which corresponds to the diameter of the zeolite Y micropore cavities (1.2 nm). Electron tomography further revealed that 3–4 nm Pt particles seem to be entrapped in the zeolite crystal, without preferential location in mesopores or at the surface of the crystals. Quantitative image analysis provided the diameters (compared with EXAFS results) and the nearest neighbor distances of hundreds of imaged Pt particles.