Provided is a production process for a graft copolymer or a thermoplastic resin composition containing the above graft copolymer, which comprises graft-polymerizing 100 parts by mass of a combination of 20 to 100% by mass of a reactive polyolefin and 0 to 80% by mass of a polyolefin other than the reactive polyolefin with 0.2 to 300 parts by mass of at least one specific monomer under the presence of a radical initiator and which is useful as a sealant, a modifier for polyolefins, a surface treating agent, a primer treating agent, a coating agent component and the like.