Ecological niche refers to the sum of the physical space, functional status, and environmental requirements occupied by species in a community. The ecological niche plays an important role in studies on community structure, interspecific relationships, and biodiversity. Based on data collected from the bottom trawl surveys in 2013-2014 in the Yellow River estuary, the spatio-temporal niche width and overlap for 12 fish species were examined using the mean crowding, niche width, and niche overlap indices. The temporal niche width indices for main fish species ranged from 0 to 1.53, which were relatively high for and relatively low for . The spatial niche breadth of the main fish species varied with season, and it was high in winter for Liza haematocheila and low in summer for . The temporal niche overlap indices among main fish species ranged between 0 and 1, and 11 species pairs reached significant ecological niche overlap. Thirty-two species pairs had low temporal overlap, occupying 46.48% of the total species pairs. This showed that the main fish species were not similarly distributed in time. Clear seasonal changes in the spatial niche overlap indices were observed for fish pairs. The spatial niche overlap indices between ranged from 0.22 to 0.86, and were high in summer and autumn and low in winter. The mean spatial niche overlap indices for all species pairs varied between seasons, they were highest in autumn at 0.17, followed by summer (0.11-0.14) and spring (0.07-0.13) and were the lowest in winter (0.07). Cluster analysis showed that all the species pairs could be divided into five groups in terms of spatial niche overlap, with relatively high niche overlap among species pairs in each group. Niche breadth and overlap for fish species was strongly related to species abundance, spatial distribution, ecological habit, and habitat conditions, which revealed the different abilities of species to effectively utilize the environmental resources in the Yellow River estuary.