Abstract: A novel star block copolymer which can be made to have a high molecular weight and gives a solution having a lower viscosity than solutions of linear polymers having the same molecular weight as the copolymer and which is expected to be used as a resist material; and a process for producing the copolymer. The star block copolymer having alkenylphenol skeletons is obtained by homopolymerizing by living anion polymerization an alkenylphenol compound in which the hydroxyl group of the phenol moiety has been protected by a saturated aliphatic protective group or copolymerizing the alkenylphenol compound with a vinylaromatic compound by living anion polymerization, subsequently copolymerizing the resultant polymer using a polyfunctional coupling agent such as divinylbenzene to obtain a star block copolymer, and eliminating the saturated aliphatic protective groups with an acid reagent.