<p>The rapid, efficient, and convenient removal of hazardous radionuclides ¹³⁷Cs and ⁹⁰Sr is an urgent need in the remediation of environmental radioactive contamination. Herein, a biomass composite membrane of K_2<i>x</i>Sn_4−<i>x</i>S_8−<i>x</i>/collagen fibers (KTS-3/CFs) was obtained by successfully loading the metal sulfide ion exchanger of K_2<i>x</i>Sn_4−<i>x</i>S_8−<i>x</i> (KTS-3) on CFs through the principle of fiber papermaking. The membrane is characterized by a homogeneous shape, operability, good water stability, and easy degradation. It exhibits satisfactory capability for removing Cs⁺ and Sr²⁺ ions, achieving maximum adsorption capacities of 82.34 mg/g for Cs⁺ and 32.98 mg/g for Sr²⁺, respectively. Meanwhile, the KTS-3/CFs membrane has fast kinetic performance and a wide pH activity range for removing Cs⁺ and Sr²⁺ ions. Further, it can still efficiently capture Cs⁺ and Sr²⁺ ions under the coexistence of K⁺, Na⁺, Ca²⁺, and Mg²⁺ ions, and even in actual water samples. The removal of Cs⁺ and Sr²⁺ ions by the KTS-3/CFs is mainly attributed to the ion exchange of Cs⁺ and Sr²⁺ with K⁺ in the interlayer spaces of KTS-3, while the CFs act as the support material for the formation of the membrane. Moreover, the KTS-3/CFs composite membrane is also capable of the fast and efficient capture of Cs⁺ and Sr²⁺ ions in a continuous filtration manner. This work not only develops an environmentally friendly, convenient, and accessible method for the preparation of metal sulfide composites but also paves the way for the development of new high-efficiency composite materials for radionuclides remediation.</p>