Several plants of Populus deltoides `R-89` exhibiting symptoms of poplar mosaic described earlier by several researchers (1,2,3) were observed in the poplar nursery of the Institute of Forest Genetics at Suweon, Korea during September, 1980. The symptoms produced a mosaic or discolored yellow spottings in mature leaves with veinal and petiolar necrosis and leaf curling (Fig. 1 and 2). Leaves with mosaic symptoms were collected and leaf-dip preparations from chlorotic area were examined for the presence of virus particles with an electron microscope. Electron micrographs of the negatively stained leaf-dip preparations revealed numerous elongated virus particles ranging 200-1300nm in length (Fig. 3). Of 156 panicles measured randomly, 68 particles (43.6%) were in the range of 660-670nm in length (Fig. 4). The values obtained fell well within the range of those described for poplar mosaic virus (PMV) by other researchers (1. 2, 3). No viruslike particles were observed from poplar leaves without mosaic symptoms. Further studies on the properties of the PMV isolate and control of the disease are underway.