The freshwater luminescent bacteria Vibrio-qinghaiensis sp.-Q67 test and the Vicia faba root tip test associated with solid-phase extraction were applied for cytotoxicity and genotoxicity assessment of organic substances in three rivers,two lakes and effluent flows from two wastewater treatment plants (WWTPs) in Xi’an,China.Although the most seriously polluted river with high chemical oxygen demand (COD) and total organic carbon (TOC) showed high cytotoxicity (expressed as TH50,the toxicity impact index) and genotoxicity (expressed as RMCN,the relative frequency of micronucleus),no correlative relation was found between the ecotoxicity and organic content of the water samples.However,there was a linear correlative relation between TⅡ50 and RMCN for most water samples except that from the Zaohe River,which receives discharge from WWTP and untreated industrial wastewaters.The ecotoxicity of the organic toxicants in the Chanhe River and Zaohe River indicated that cytotoxic and genotoxic effects were related to the pollutant source.The TⅡ50 and RMCN were also found to correlate roughly to the dissolved oxygen concentration of the water.Sufficient dissolved oxygen in surface water is thus proved to be an indicator of a healthy water environmental condition.