<p><P>PROBLEM TO BE SOLVED: To provide a treating agent for ship's ballast water exhibiting excellent killing properties against organisms contained in ship's ballast water, the organisms including bacteria and aquatic microorganisms such as planktons, and further, the treating agent being stable and causing little corrosion. <P>SOLUTION: The treating agent for ship ballast water is a mixture which is obtained by adding a phosphoric acid salt and sodium hydroxide to a sodium hypochlorite solution and which has a pH of 10 to 13. It is preferable that the phosphoric acid salt is added in such the amount that the weight ratio of available chlorine to phosphoric acid (PO<SB POS="POST">4</SB>) falls within the range of 30:1 to 2:1. <P>COPYRIGHT: (C)2013,JPO&INPIT</p>
