Objective To study the DNA damage effect of the organic extracts from Chlorinated domestic sewage coming from three different places in vivo and in vitro. Methods The domestic sewage samples were collected from different places:university A, university B and a hotel. The DNA damage effect was tested in the bacteria, cells and BALB/C mouse by single cell gel electrophoresis (comet assay), the micronucleus test, Ames test. Results Comet assay indicators:all three samples, before chlorinated, at the dosages of 1.0, 5.0 mg/ml, after chlorinated, at the dosages of 0.04, 0.2, 1.0, 5.0 mg/ml for university A, 0.2, 1.0, 5.0 mg/ml for a hotel, 1.0, 5.0 mg/ml for university B, were significantly higher than those in the negative group(P