Abstract: To study the effects of the trophic position of fish in food web on the structure and to examine the composition, richness, diversity in infracommunities of helminth communities in the alimentary tracts, the mandarin fish Siniperca chuatsi were collected from three lakes in the flood plain of the Yangtze River, China. Eleven species of helminths were recorded from the three localities. The dominant species of communities in these three lakes was the trematode Dollfustrema vaneyi. 65 percent of individuals were infected with 1 or 2 parasite species, and the highest infection rate of parasite species was 6. Mean species richness and the Brillouin's index in the three lakes were 1.532.13 and 0.120.33, respectively, with the highest Brillouin's index in the Poyang Lake. The values of percentage similarity index and Jaccard's similarity index between the Liangzi and Dongting lakes were the highest. Compared with the fish in different positions in food web, the richness and diversity of helminth infracommunities in alimentary tracts, the predatory mandarin fish S. chuatsi were dramatically higher than those of the herbivores and omnivores. In addition, the effects of feeding habit on the structure of parasites communities were discussed.