Abstract:Benthic macroinvertebrates and hydrochemical indices were collected from 66 sampling sites in the Pearl River Basin in the years 2011 and 2012. The benthic macroinvertebrate communities and hydrochemical indices from 11 sites of the Beijiang River and 17 sites of the Yujiang River in the year 2011 were investigated, and the integrated environmental factors(PC1 and PC2)were obtained through principle analysis. Based on analysis of the correlation between 36 candidate parameters and the environmental factors, and the distribution of the parameters, three indices applicable to bioassessment of the river ecosystem in the Pearl River Basin were determined, including the percentage of diptera taxa, the percentage of scrapers, and the biotic index(BI). Then, the integrated biotic index was determined and the grading scales were classified into non-pollution, slight pollution, moderate pollution, and heavy pollution categories. The assessment of integrated biotic indices from 66 sampling sites shows that the biological conditions of 80. 3% of the rivers had the status of slight to moderate pollution, 13. 6% of the rivers had the status of non-pollution, and 6% of the rivers had the status of heavy pollution in the Pearl River Basin. This study demonstrates the applicability of bioassessment of water quality in medium-and large-sized rivers of the Pearl River Basin using benthic macroinvertebrates.