Abstract: Tomato zonate spot virus (TZSV) and Potato virus Y (PVY) commonly co-infect the same plant under natural conditions. We compared the pathological characterization resulting from mixed and single infection of tobacco. Cells with mixed infection showed increased number of TZSV particles, and the particles clustered into the vesicles to form inclusion bodies, which cross-distributed in the cytoplasm with pinwheel and laminated inclusions and particles. The number of mitochondria was increased. The structure of mitochondria, chloroplasts, and the nucleus maintained relative integrity. The number of particles, inclusion bodies, and inclusions was increased but did not cause more severe damage on the subcellular structure when TZSV or PVY co-infected the same tobacco plant. A synergism may exist among TZSV, PVY and the plant host during co-infection.