To provide a hair composition, capable of excellently keeping a hair style with the elapse of time, without being accompanied with stickiness, and capable of being easily removed by a shampoo, to provide a nail enamel having excellent adhesion and abrasion resistance, without being accompanied with the stickiness, to provide a makeup composition optimal in adhesion to the skin and comfortable, and to provide a cosmetic composition being prevented from the stickness under a highly humid condition.

A straight-chain block ethylenic copolymer contains at least one block A and at least one block B, wherein the block A is prepared from monomers comprising an ethylenic monomer with a lactam ring corresponding to formula (I) in an amount of 52-99 wt% and at least one ionic hydrophilic monomer in an amount of 1-48 wt% and the block B is prepared from monomers not containing the ethylenic monomer with the lactam ring corresponding to formula (I) or containing the ethylenic monomer in a small ratio.