Distribution of Sm and Ce in mice was investigated after inhalation exposure to their oxide particles of 5 μm diameter and 15 mg/m3.Sm and Ce were mainly distributed in lung,their concentrations decreased with passing time,and their concentrations in lung were correlated with exposure periods.Concentrations of Ce were lower than that of Sm in each point.Sm was also distributed in the other organs and bone but Ce was scarcely detected.These results suggest that the behaviors of Sm and Ce inhaled were different,although their chemical properties are similar. Distribution of Sm and Ce in mice was investigated after inhalation exposure to their oxide particles of 5 μm diameter and 15 mg / m3.Sm and Ce were mainly distributed in lung, their concentrations decreased with passing time, and their concentrations in lung were correlated with exposure periods.Concentrations of Ce were lower than that of Sm in each point.Sm was also distributed in the other organs and bone but Ce was scarcely detected.These results suggest that the behaviors of Sm and Ce inhaled were different, although their chemical properties are similar