Objective To study the effects of PVC_U pipes on tap water quality.Methods The safty assessment on a certain brand of PVC_U pipes was carried out. A residential quarter with this kind of PVC_U pipes for water supply was selected. Drinking water samples were collected from 2 pipeline inlets outside the quarter and 4 outlets inside the apartment. The indexes such as organoleptic indexes, general chemical indexes, heavy metals, organic compounds, radioactivity of the water samples were determined. The toxicological tests were carried out also. Results The sanitary indexes of the water samples for immersing PVC_U pipes except the content of ferrite accorded with the related national standards. No significant differences were observed in sanitary indexes of the water samples collected from inlets and outlets of pipeline for the apartment. The organic extracts of the water samples from the outlets of water supply system in the apartment showed negative results in acute oral toxicity test, 30_day feeding test, micronucleus test and Ames test. Conclusion PVC_U pipes were safe and hygenic for drinking water supply.