The present invention provides a novel block copolymer that can be used as a surface treatment agent that can impart various properties such as dispersibility to objects such as inorganic particles. The block copolymer of the present invention includes a hydrophobic segment and a hydrophilic segment. The hydrophobic segment includes a monomer unit composed of at least one monomer selected from the following formulae 1 and 2. The hydrophilic segment Contains a monomer unit composed of a monomer of the following formula 3: In Formula 1, R 1 is hydrogen or methyl, and m is an integer from 0 to 21. In Formula 2, R 1 is hydrogen or methyl, R 2 and R 3 are each independently an alkyl group having 1 to 6 carbon atoms, m is an integer of 1 to 6, and n is an integer of 5 to 70. In Formula 3, R 1 is hydrogen or methyl.本發明提供一種可用作可對無機粒子等對象物賦予分散性等各種特性之表面處理劑之新穎之嵌段共聚物。本發明之嵌段共聚物包含疏水性鏈段及親水性鏈段，疏水性鏈段包含由選自下述式1及式2中之至少一種單體所構成之單體單元，親水性鏈段包含由下述式3之單體所構成之單體單元：式1中，R1為氫或甲基，且m為0~21之整數，式2中，R1為氫或甲基，R2及R3分別獨立地為碳原子數1~6之烷基，m為1~6之整數，且n為5~70之整數，式3中，R1為氫或甲基。
