Poly(vinyl acetate) chains end-capped by a Co(acac)(2) complex [PVAc-Co(acac)(2)] were prepared by bulk cobalt-mediated radical polymerization (CMRP) of vinyl acetate and used for grafting fullerene (C60) with four PVAc arms at low temperature (30 degrees C). A photoactive water-soluble poly(vinyl alcohol)/C60 nanohybrid was then prepared by hydrolysis of the PVAc arms of the nanohybrid. Because of photoactivity and very low cytotoxicity, this type of water-soluble nanohybrid is very promising for the photodynamic cancer therapy.