Abstract: After investigating the zoobenthic community in 16 main tributaries of the Wujiang River, Guizhou Province, 78 species were obtained, belonging to 4 phyla, 7 classes, 17 orders and 39 families, with 22-21,712 individuals per square meter. Species compositions and individual numbers of zoobenthos in the Weng’an River and its downstream tributaries were more abundant than those in the upstream tributaries. Studies on community similarity showed that while arthropods were dominant in the upper tributaries, mollusks were dominant in the middle and lower tributaries. Community structures were similar among the upper tributaries, but were quite different among the middle and lower tributaries. Assessment of potential ecological risk caused by mercury in the sediments was conducted according to Hakanson’s method, and the results demonstrated that the risk degrees were from slight to heavy levels in the river valley. Negative and no significant correlations were found between Hg Potential Ecological Risk Index and species number and density of zoobenthos (R-0.32, -0.12， P＞0.01); therefore, the effect of mercury pollution on zoobenthos in the river valley should be further investigated.