Yolk/shell composites with a movable Fe3O4 core inside the hollow polypyrrole (PPy) capsules were obtained through a template-assistant selectively etching method. The Fe3O4 nanoparticles were firstly synthesized according to the solvothermal method. Then, SiO2 shell was coated on the Fe3O4 nanoparticle surface by a sol-gel reaction. Subsequently, the PPy shell was covered on the surface of as-prepared Fe3O4@SiO2 composites and sandwiched Fe3O4@SiO2@PPy composites formed. After selectively etching the middle SiO2 layer, the yolk/shell Fe3O4@PPy composites were obtained. Both the PPy and SiO2 shell thicknesses could be readily turned during the preparation. The influence of poly(N-vinylpyrrolidone) on coverage of PPy shell onto Fe3O4@SiO2 composites surface was studied in detail. Yolk/shell Fe3O4@PPy composites were used as supports for deposition of Pd nanoparticles. Pd nanoparticles were densely and uniformly anchored on both outer and inner surface of PPy shell due to the coordination interaction between amino groups on PPy backbone and Pd2+ ions. Fe3O4@PPy/Pd catalysts showed excellent catalytic activity towards the reduction of methylene blue dye with sodium borohydride as reducing agent. In addition, such catalysts could be easily separated from reaction solution and reused due to the magnetic property originated from the Fe3O4 core. (c) 2013 Published by Elsevier B.V.