Aquatic ecotoxicity of bisphenol A, a well-known endocrine disrupter in mammals, was studied using laboratory-reared Daphnia magna as a test organism. The static acute 48 h EC50 of bisphenol A for daphnid neonates(<24 h old) was 12.9mg/l and 110 h LC50 values of bisphenol A for daphnid embryos of different ages after deposition into the brood chamber increase with ages in the range of 1.55mg/l-8.91mg/l. Also, 48 h EC50s generally increase with daphnid s ages in the range of 12.9mg/l-19.8mg/l. In the acute toxicity tests using mature daphnids, the lethal response and immobility all showed good concentration-response relationship with exposure concentration and exposure time, showing little difference between lethality and immobility. These results clarify that acute toxicity tests, using daphnid and its embryo, could also be useful tools easily available for the assessment of ecotoxicity of various harmful chemicals.