Abstract: Newcastle disease（ND） is recognized as one of the most important poultry diseases in the world. Along with the extensive use of live vaccine against NDV，newcastle disease virus isolated from the field is often a combination of different newcastle disease. In order to avoid the interference among different strains，it is necessary to purify and distinguish the different NDV strains through the plaque. Newcastle GM2 isolates were purified by plaque-purification in this study，and the biological characteristics of the virus before and after plaque-purification were determined. The result showed that MDT，ICPI，IVPI of the Newcastle GM2 isolates before plaque purification was 50.5，1.78 and 2.41，whereas after plaque-purification MDT，ICPI，IVPI was 47.5，1.89 and 2.65，respectively.

Key words: newcastle disease virus, plaque-purification