Sorption experiments of Pu-IV on synthetic Mn oxide were made in 0.1 M NaCl + 0.1 mM sodium citrate solutions under acidic to alkaline pH conditions. As the results of the sorption experiments, Pu was efficiently removed from the solutions under neutral pH conditions, where Pu forms the stable 1:2 Pu-IV-citrate complex. Furthermore, it was demonstrated that Pu-IV was oxidized to Pu-V and Pu-VI on Mn oxide.