AbstractMagnetic cellulose fiber composites were prepared by a “vacuum-lumen-loading” method with polyethylenimine (PEI) as retention aid. The composites thus formed preserved the inherent properties of the cellulose fiber and gained the magnetically responsive properties of nanoparticles. Magnetic paper was further made from the composites. These materials were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, a vibrating sample magnetometer, and paper testers. There was a large amount of magnetic nanoparticles deposited on the exterior, in the pores, and especially in the lumen of fibers. Lumen loading of nanoparticles is favored by pulp beating, silica shell modification of magnetite, vacuum conditioning, and usage of PEI. The physical strength of paper was reduced to a certain extent because of unavoidable deposition of nanoparticles on the exterior of fibers, which could block the formation of hydrogen bonding between fibers. Our results show that both the cellulose fiber composites and the resulting paper possessed good superparamagnetism with tiny remnant magnetization and coercivity. These materials will allow the investigation of new concepts in paper making and packaging, security paper, and information storage.