Laizhou Bay, an estuary of the Yellow River, is one of the three most important bays of the Bohai Sea, China. It is characterized by a high level of primary productivity and is one of the most important spawning and feeding grounds for most fish species in the Yellow Sea and Bohai Sea. After decades of overfishing, the dominant species of the fish assemblage have been altered. Ecological niche describes how an organism or population responds to the distribution of resources. Therefore, studies on ecological niches are extremely important to clarify the ecological dynamics of different species and the mechanism of interspecific coexistence and competition, as they are a fundamental tool for the conservation and assessment of fish stocks, as well as for the analysis of the ecosystem as a whole. Data were obtained from a bottom trawl survey conducted in Laizhou Bay (119°05'-120°00'E, 37°12'-37°40'N) in 2011. The most dominant species that contributed to 97.2% of biomass and 98.4% of abundance were used for the hierarchical cluster analysis, non-metric multidimensional scaling (NMDS), principal component analysis (PCA), and spatio-temporal niche analysis. Tissue samples were collected from the 12 most dominant species recorded in the trawl-survey catches. δ¹³C and δ¹⁵N stable-isotope analyses were performed to assess the trophic niche. A total of 49 fishes were collected. The assemblage density of dominant species was low in the summer and winter and high in the spring and autumn. The mean crowding of the dominant species was low in the spring and winter, and high in the summer and autumn. The results of the hierarchical cluster analysis based on the Euclidean distance showed a similarity with the results of the ecological dominance analysis. The PCA showed that Sardinella zunasi was one of the species that mostly affected the first axis, and Thryssa kammalensis mostly affected the second axis. Callionymus beniteguri had the highest value of tempo-spatial niche width, followed by Platycephalus indicus, Tridentiger barbatus, and Cynoglossus joyneri. Significant overlap of spatio-temporal niche occurred between the seven groups:Pennahia argentata vs. Setipinna taty (0.798), S. taty vs. Johnius belangerii (0.793), C. joyneri vs. J. belangerii (0.771), Chaeturichthys stigmatias vs. J. belangerii (0.770), Konosirus punctatus vs. Scomberomorus niphonius (0.763), and K. punctatus vs. C. joyneri (0.625). Konosirus punctatus had the highest δ¹³C range (CR=9.2), and J. belangerii had the highest δ¹⁵N range (NR=7.1). The total area (TA) of the trophic niche of S. zunasi and K. punctatus were the highest, both being larger than 20. Johnius belangerii had the lowest TA (1.38); however, it had a significant overlap with other species, such as C. stigmatias, C. joyneri, and P. argentata. The results showed a similar trend with cluster analysis, NMDS, and PCA; however, the trend was different with the tempo-spatial niche analysis. The non-migration species, which lives throughout year in the bay, with lower assemblage densities had a higher value of spatio-temporal niche width. The seasonal migratory species had a lower tempo-spatial niche width because of the low temporal niche width. The high spatio-temporal niche overlap between the most dominant species found in this study also reflected a high degree of homogeneity of fish assemblies in the Laizhou Bay. Competition owing to niche overlap was not the decisive factor that formed the community structure of nekton in the Laizhou Bay. The community structures might be most affected by anthropogenic activities.