Abstract: As phenolic compounds such as pentachlorophenol(PCP), 2,4-dichlorophenol(2,4-DCP), 2,4,6-trichlorophenol(2,4,6-TCP), 4-nitrophenol(4-NiP), 2,4-dinitrophenol(2,4-DNP) and 2-methyl-4,6-dinitrophenol are frequently detected in the surface water of China and 2-methyl-4,6-dinitrophenol is also listed as a priority pollutant for monitoring in the USA, evaluation was performed of those compounds for ecological hazards, using the species sensitive distribution (SSD) approach and the assessment factor (AF) approach, based on the acute toxicity endpoints, the chronic lethal endpoints and the chronic non-lethal endpoints. On the basis of concentrations of these compounds measured in the lakes and rivers typical of China, chronic ecological risk quotients (RQ) of PCP, 2,4-DCP, 2,4,6-TCP and 4-NiP were worked out. Results show that the HC₅(hazardous concentration for 5% of the species) of PCP and 2,4-DCP derived by the chronic non-lethal endpoints was obviously lower than that derived by the chronic lethal endpoint. Furthermore, the ecological risks of PCP, 2,4-DCP, 2,4,6-TCP and 4-NiP in the Taihu lake, Songhua River, Yangtze River, Pearl River, Liaohe River, Haihe River, Yellow River, Huaihe River, and the Qiantang River system, were all at acceptable level. However the long-term hazardous risk of PCP in these waterbodies should arouse close attention, especially to its chronic non-lethal hazard to reproduction, development and growth of the aquatic organisms as its RQ is very close to 1.