Abstract: We studied the diet of Whooper Swan (Cygnus cygnus) from field survey of plants and microhistological analysis of feces. The study was conducted from February to April 2013 in the Nanhaizi Wetland of Baotou. The results showed that: Whooper Swan spring-diet mainly constituted dockleaf knotweed(Polygonum lapathifolium), corn (Zea mays), liquorice (Glycyrrhiza glabra) and common cattail (Typha latifolia). We found a significant difference in the the frequency of each plant consumed in different migratory periods by Whooper Swan. Before the ice of Yellow River is melted, the first eighteen migrating Whooper Swans mainly fed on dockleaf knotweed, accounting for 99.4%. ; After the ice of Yellow River is melted, one hundred and twenty Whooper Swans immigrate again, mainly feeding on corn, accounting for 69.7% of their diet followed by liquorice and common cattail in relatively small proportion, 18.3% and 11.2%, respectively. These results suggest that there is a close relationship between the wetland dominant plants species and agricultural products on the feeding behaviour of Whooper Swans .