Abstract: ObjectiveThe differences in microstructures of down feather of different swimming bird species were re-searched in order to provide scientific evidence for the identification of swimming bird species.MethodSix swimming bird species were gathered as research objects including Anas platyrhynchos,Cygnus columbianus,C. atratus,Podiceps grisegena, Larus crassirostris ,and Phalacrocorax carbo. A. platyrhynchos,C. columbianus and C. atratus were from order of Anseri-formes;P. grisegena was from order of Podicipediformes;L. crassirostris was from the order of Lariformes and P. carbo was from order of Pelecaniformes. Scanning electron microscope(SEM)was used to observe nodule morphology on barbules from belly down feather of the six species,and analyze the difference in distance between nodules and the nodular diameter.ResultThe belly down feathers of the six swimming bird species were composed of nodular barbules. The distribution of barbules was loose. There were obvious differences in nodule shape and distance between nodules among different bird species. There were mainly four typical morphologies,A. platyrhynchos and P. carbo had the same kind of morphology. C. columbianus and L. crassirostris had another kind of morphology. P. grisegena and C. atratus had two different morphologies respectively. These six swimming bird species also had some differences in the distance between nodules and nodule diameter of barbules from down feather. The distance between nodules of barbules from belly down feather in A. platyrhynchos was longer than that of other five swimming bird species. The distance between nodules of barbules from belly down feather in C. columbianus was the shor-test. The nodular diameter of barbules from belly down feather in P. grisegena was the largest. And the barbules from belly down feather in P. carbo had the smallest nodular diameter.ConclusionThere are differences in the structure of barbules from down feather in different ecological groups of bird species. The nodule morphology of barbules from belly down feather can be observed by SEM. By combining the morphology with the difference in distance between nodules and nodular diameter,the six swimming bird species including A. platyrhynchos,C. columbianus,C. atratus,P. grisegena,L. crassirostris ,and P. carbo can be basically distinguished.