Ag-Os, water treatment agent, was administered orally to ICR mice and Sprague-Dawley rats to investigate the acute oral toxicity. $LD_{50}$ values were above 5 g/kg, 2,000 fold higher than the expected concentration in water, in both species with oral administration. There were also no differences in body weight changes, clinical signs and atopsy findings between all treated groups and control group. Therefore, it was concluded that Ag-Os is a very safe compound.