Faraday rotation spectrum has been measured at room temperature in a magnetic nanocomposite of&ggr;-Fe2O3/SiO2.The material consists of isolated&ggr;-Fe2O3nanoparticles dispersed in a silica matrix, and it was prepared through a sol-gel method. The composite contains 18&percent; of&ggr;-Fe2O3in weight with an average particle size of 20 nm. It has a coercitivity of 30 Oe and anMSof 6 emu/g. The specific Faraday rotation spectrum exhibits a narrow peak centered around 765 nm, reaching a value of 110°/cm and an absorption coefficient of64 cm−1.Faraday rotation versus applied field has also been measured, and a cycle similar to the one described by the magnetization has been found. ©1997 American Institute of Physics.