A luminescent superparamagnetic nanocomposite with an Fe 3 O 4 -SiO 2 -CdS structure is synthesized. Coated with a silica shell, Fe 3 O 4 nanoparticles and CdS quantum dots (QDs) are successfully assembled together. Analysed from the test results of X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), hysteresis loop, and photoluminescence (PL) spectrum, these nanocomposites exhibit superparamagnetic and photoluminescent properties.