Many studies on free-living marine nematodes were carried out in Chinese seas, but the taxonomic diversity of nematodes was seldom reported. A benthic survey with fifteen stations was conducted in Tianjin offshore (Fig. 1) in spring 2007, and the taxonomic distinctness of nematodes was analyzed based on the nematode samples. A total of 87 nematode species belonging to 2 classes, 2 subclasses, 5 orders, 7 suborders, 14 families and 39 genera were identified in this cruise, excluding the juvenile and incomplete individuals. The majority of nematodes belonged to Chromadorea, which included 74 species and accounted for about 85% of all nematode species. Two taxonomic indices, the average taxonomic distinctness index (Δ+) and the variation in taxonomic distinctness (Λ+) of nematode assemblage, were calculated with PRIMER software. The results of Δ+ and Λ+ in each station were listed in Table 1. The theoretical average value of Δ+ and Λ+ were 60.5 and ca. 420, respectively. The values of Δ+ varied with station, which ranged from 49.8 to 63.0; the fluctuation of Λ+ was huge, from 233 to 514. The two indices indicated that the nematode assemblages had big changes along with the station. The funnel plots, Fig. 2 and 3, showed that the taxonomic distinctness of nematode assemblages was lower in the coastal southwest area, indicating that the environment was disturbed. The taxonomic distinctness of nematodes in these four stations was affected by some chemical factors, and was related to the particle size and chlorophyll a content of sediment, too. Compared with four traditional diversity indices, the average taxonomic distinctness index was more sensitive to environmental difference. The results indicated that Δ+ and Λ+ were good indices to reflect the variations of nematode assemblage and environment.