Biochar-immobilized potassium nickel hexacyanoferrate (KNiFC) as a sorbent for removal of radioactive cesium (Cs) from aqueous solutions was prepared using a novel method. Japanese cedar sawdust loaded with NiSO 4 using a ball mill was carbonized at various temperatures. The resultant Ni-loaded biochar was immersed in a K 4 [Fe(CN) 6 ]•3H 2 O solution, and biochar-immobilized KNiFC was obtained. For comparison, Ni-loaded biochar was also prepared using the impregnation method. The loading of Ni using the ball mill resulted in a higher Ni amount in the biochar compared with the impregnation method. The carbonization at 400 °C was suitable for Cs adsorption on biochar and synthesis of KNiFC. Consequently, KNiFC immobilization on biochar improved the Cs sorption performance in aqueous solutions with Na + , K + , Ca 2+ , Mg 2+ , and Cs + . The sorption performance was selective in aqueous solutions with radioactive Cs and other cations of high concentration. HighlightsLow-cost Cs adsorbent was prepared using a novel method from bioresource and KNiFC. The application of ball mill was effective for loading Ni on biochar. Immobilization of KNiFC on biochar improved Cs sorption performance. Removal of 134 Cs and 137 Cs using biochar-immobilized KNiFC was selective.