The grafting of branched polymers onto vapor grown carbon fiber (VGCF) surface and their electric properties of the composite prepared from the branched polymer-grafted VGCF were investigated. In the first step, the grafting of copolymers having pendant peroxy groups onto VGCF was achieved by the copolymerization of 1-(t-butylperoxy-i-propyl)-3-i-propenylbenzene (BPPB) with vinyl monomers initiated by the system consisting of Mo(CO)(6) and trichloroacetyl groups previously introduced onto the surface. In the second step, the postpolymerization of vinyl monomers was initiated by pendant peroxy groups of grafted poly(vinyl monomer-co-BPPB) on the surface to give branched vinyl polymer-grafted VGCF. The dispersibility of VGCF in THF was remarkably improved by grafting of branched polymers onto the surface. The electric resistance of composites prepared from the branched polymer-grafted VGCF suddenly increased when the composites were transferred into solvent vapors and suddenly decreased when they were transferred to dry air.