The present invention provides a new star-shaped block copolymer and a production process therefor, wherein the new star-shaped block copolymer has high heat resistance despite having a low viscosity. It has been found that a new star-shaped block copolymer has high heat resistance wherein the new star-shaped block copolymer comprises a plurality of star-shaped structures 1 in which at least three chain polymer segments 2 are radially extended from a central polyvalent mercaptan segment 3, wherein the star-shaped structures 1 are bonded to each other through a bonding structure 4 at their chain polymer segments. In addition, in a production process for a star-shaped block copolymer comprising the multistep radical polymerization in the presence of a polyvalent mercaptan wherein the elementary steps of the multistep radical polymerization differ in polymerizable monomers as used therein, the improvement according to the present invention is characterized in that at least one of the elementary steps of the multistep radical polymerization involves the joint use of a polyfunctional monomer with the polymerizable monomer.