Recoverable platinum nanocatalysts immobilized on magnetic spherical polyelectrolyte brushes (MSPB) were synthesized and characterized by high resolution transmission electron microscope (HRTEM), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). High catalytic activity was found by photometrically monitoring the reduction of 4-nitrophenol by NaBH4 in the presence of MSPB-Pt composites. An excellent stability and recyclability of catalyst was observed after consecutive eight runs following by external magnetic-separation and redispersion. This novel approach provides an excited potential application in preparation of recyclable metal nanocatalysts with high activity.