Abstract: Ducks intramuscularly inoculated with two avian influenza virus isolates, A/duck/Guangdong/221/2004（H5N1）and A/duck/Guangdong/185/2004（H5N1）, had micropathological and ultrapathological lessions in some degree in multiple organs, such as the damages of mucous membrane of respiratory and alimentary tract, and hyperemia, congestion, hemorrhage, edema, and cell degeneration, necrosis, inflammation or a combination of these features in the heart, liver, lung, kidney, and encephalon etc, but did not died in two weeks.

Key words: H5N1 subtype avian influenza; pathology; ducks