Chitosan nanoparticles with magnetic properties can be potentially used in drug delivery systems. Different from the traditional surfactants, the novel magnetic Ni0.5Mn0.5Fe2O4-chitosan nanoparticles has the advantage of excellent biodegradation and a high level of controllability. The Ni0.5Mn0.5Fe2O4-chitosan nanoparticles with a core-shell structure were prepared successfully. The transmission and scanning electron microscopy images showed that the cubic-shape magnetic Ni0.5Mn0.5Fe2O4 particles were encapsulated by the spherical chitosan nanoparticles. The size of the Ni0.5Mn0.5Fe2O4-chitosan nanoparticles were all below 100 nm. The saturated magnetization of the Ni0.5Mn0.5Fe2O4-chitosan nanoparticles could reach 80 emu/g and showed the characteristics of superparamagnetism at the same time. The amount of bovine serum albumin (BSA) released from the particles at different time intervals was estimated by the UV spectrophotomertic method. The dissolution profile and in vitro release kinetics showed that Ni0.5Mn0.5Fe2O4-chitosan nanoparticles were promising for controlled delivery of the drug.