A novel kind of biocompatible pH- and temperature-responsive magnetic nanoparticle consisting of iron oxide nanoparticles coated with pH-responsive chitosan oligosaccharide and temperature-responsive poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer was developed. The particles were characterized by TEM, DLS, VSM, FTIR spectroscopy, and TGA. The results indicated that the self-aggregation of the prepared nanoparticles was not only caused by the thermoinduced self-assembly of the immobilized block copolymers, but also affected by the pH-induced charge property change of the particle surface. The self-assembled behaviors can be readily reversed by adjusting the pH or temperature value. Thus, the attractive properties of reversible and controllable dual-responsive self-assembly might endow the biocompatible magnetic nanoparticles with potential applications in biomedical fields such as DNA delivery, drug targeting, and tissue engineering.