Abstract: The fracture of brass nut for connecting tap and water meter lead to pipeline leakage at a residence. The fracture analysis was made by means of macroscopic and scanning electron microscope. Experiment results showed that the fracture of the nut was caused by foundry defects such as holes,shrinkages .And redundant lead in brass nut which formed fragile eutectic omentum in grain boundary was another reason of the fracture.