Controllable magnetic Ag@Ni core-shell nanoparticles (NPs) have been designed and constructed on the bayberry tannin (BT) grafted skin collagen fiber (SCF) though a simple one-step route. Due to the mild and naturally occurring reduction ability of BT, when the SCF-BT made contact with the mixture of Ag + /Ni 2+ solution, BT was able to preferentially reduce Ag + into Ag NPs, and subsequently, the formed Ag NPs served as in situ seeds for the over growth of magnetic Ni shell by the reduction of NaBH 4 . The systematic TEM and EDS analysis confirmed that the as-prepared Ag@Ni NPs on SCF-BT were a typical core-shell structure. Magnetic study of core-shell NPs indicated that their magnetic properties could be tuned by modulating their shell thickness with the change of Ag + /Ni 2+ molar ratio. The diameter and size distribution of SCF-supported Ag@Ni core-shell NPs also can be controlled by varying the grafting degree of BT on SCF, as characterized by TEM. A novel and important application of these SCF-supported Ag@Ni core-shell NPs composites is use as high-performance microwave absorption materials in the whole X-band, C-band and some part of S-band with maximum reflection loss (RL) of À51 dB. The further analysis of electromagnetic parameters indicated that the enhancement of dielectric loss properties of SCF-supported Ag@Ni core-shell NPs is introduced by the multiple defective site polarization and interfacial polarization in bimetallic interface. In addition, owing to the combinated magnetic property on the nickel shell, the SCF-supported Ag@Ni core-shell NPs also exhibited a significant eddy current effect and anisotropic energy effect for the microwave absorption. To the best of our knowledge, this is the first time to explore tailoring the magnetic property, electromagnetic property and microwave absorption performance of functional core-shell NPs by tuning their core-shell microstructures. The present work has a significant potential for the development of novel, lightweight, low-cost, flexible and highly efficient microwave absorbing materials.