Abstract: To explore the early selection method for Poplars to resist the infection of Coryneum populinum Bres., a study was conducted in the seriously infected nursery of Dalinghe Forest Farm, Jin County, Liaoning Province. According to the incidence rate and index, a total number of 10 Poplar clones of heavily-infected, medium-infected and resistant ones were selected for in vitro culture. In petri dishes, the spreading leaves of the tissue-cultured Poplar clones were selected for inoculation. A drop of the spore suspension with a concentration of 2×104 spores/ml was dropped at both sides of the main veins of the leaves. Electron microscope and scanning electro-microscope were used periodically to observe the changes of the leaves. The results show:(1) these clones are sensitive to the inoculated fungus; (2) there is a big difference in disease-resistance among the differing clones, and the infection degree is in accordance with that in the field. After inoculation the tissue cultured clones of resistant ones in the field No. 1, 2 and 3 are not infected and their hyphae don't invade the inner tissue of the leaves either. Those of the medium-infected clones: No. 5 and 6, after inoculation, appear a few yellowish-brown spots, while those of the heavily-infected clones: No. 7, 8, 9 and 10 after inoculation appear brown necrogenous spots, and the young saplings wither. This illustrates that it's possible to use in vitro culture method to conduct early testing for disease resistance.