Bioaccumulation and biosorption of 137Cs, 233U, 239Pu, 241Am, 90Sr and 237Np by Arthrospira platensis CNMN–CB-02 biomass were investigated. Bioaccumulation experiments were performed in EDTA-free Zarrouk cultivation medium and in the medium with the addition of sodium polyphosphate. Arthrospira platensis CNMN–CB-02 biomass showed high uptake capacity for 239Pu, 241Am, and 90Sr in both media, while the uptake of 233U was significantly enhanced in the presence of polyphosphate ions. In biosorption experiments, the biomass also showed high sorption capacity for 239Pu, 241Am, and 90Sr and low for 233U. The amount of 137Cs removed from the solution by living and dry biomass was almost the same. The desorption studies revealed that A. platensis CNMN–CB-02 biomass can be reused for biosorption and showed a high strength of radionuclide binding to phosphorylated biomass. A. platensis CNMN–CB-02 biomass can be considered a good candidate for radionuclide removal from salt and alkaline solutions and in in situ bioremediation strategies.