The present invention provides a surface treatment agent, which is hydrophobic at a dry state and gradually becomes hydrophilic when being contacted by water, to thereby have both of makeup durability and washable property. Specifically, the present invention provides a surface treatment comprising a first block copolymer represented by the general formula (1).(In formula (1), R1, R2 each independently represents an alkyl group, a polyoxylalkylene group, an acryl group, a phenyl group or an aralkyl group, X represents an alkyl chain with 1 to 18 carbon atoms in which the non-adjacent carbon atoms may be represented by an oxygen atom to form an ether, Y represent a single bond or divalent connecting group, Z1 represents a hydrogen atom or a methyl group, n, m represent the degree of polymerization)本發明係提供一種表面處理劑,即藉由乾燥時為疏水性,與水接觸時慢慢變為親水性,從而化妝保持性與沖洗性並存。具體而言,為含有下述通式(1)表示的第1嵌段共聚物的表面處理劑。(式(1)中,R1、R2各自獨立地表示烷基、聚氧伸烷基、醯基、苯基、芳烷基,X表示不鄰接的碳原子可被氧原子取代從而形成醚的碳原子數1至18的烷基鏈,Y表示單鍵或2價的連接基,Z1表示氫原子或甲基,n、m表示聚合度)1‧‧‧Q片段2‧‧‧PTMC片段
