Abstract: Sargassum fusiforme was immobilized with calcium alginates and its biosorption property to 239Pu was studied by batch and column methods. Biosorption equilibrium time of immobilized Sargassum fusiforme biosorbent to ²³⁹Pu is 120 min and biosorption efficiency is over 99.2% when the initial concentration of ²³⁹Pu is 21.5 kBq/L and pH is 2.5-5.0. After five repetition biosorption-desorption cycles biosorption efficiency is still over 98.0% when the velocity of flow is 2 mL/min in column experiment. Immobilized Sargassum fusiforme biosorbent is better to ²³⁹Pu due to its better chemical stability, mechanical strength, lower cost, high biosorption efficiency and repeated biosorption-desorption cycles.