Based on the data from beam-trawl and singletrawl surveys conducted in the April (spring), July (summer), and November (autumn) of 2011, this paper studied the seasonal variations in the community structure and biodiversity of nektons in the Xiangshan Bay. A total of 96 nekton species were collected, including 54 species of fish, 38 species of crustaceans, and 4 species of cephalopods. Acanthopagrus schlegelii, Lateolabrax maculates, and Mugil cephalus were the most commercially important species in the Bay. In different seasons, the biodiversity indices including species diversity (H′'), species richness (D), and evenness (J′) showed no significant differences, but the community structure in summer differed significantly with that in spring and autumn. Some migrant species, such as Pennahia argentata and Portunus trituberculatus, only appeared in the bay in summer to spend their nursing periods, which, together with the seasonal variations in the percentage contributions of some dominant species to the total biomass, could be the main factor inducing the seasonal variation in the species composition of the nekton community. The abundance and biomass curves (ABC) indicated that the nekton community in the Bay was moderately disturbed, and the fastgrowing, small-sized, and opportunistic
 r-selected species occupied the dominance in the nekton community.