The present invention provides an organopolysiloxane obtained by binding, to at least two silicon atoms of an organopolysiloxane segment constituting a main chain, a poly(N-acylalkyleneimine) segment composed of a repeating unit represented by the following formula (1): wherein R 1 represents a hydrogen atom or an alkyl group having from 1 to 3 carbon atoms and n is 2 or 3, via an alkylene group containing a hetero atom, wherein the poly(N-acylalkyleneimine) segment has a number-average molecular weight of from 1,600 to 3,500； a mass ratio (a/b) of the organopolysiloxane segment (a) constituting the main chain to the poly(N-acylalkyleneimine) segment (b) (which will hereinafter be called "mass ratio (a/b)", simply) is from 42/58 to 58/42； the organopolysiloxane segment between two poly(N-acylalkyleneimine) segments adjacent to each other has a weight-average molecular weight of from 1,600 to 3,500； and the organopolysiloxane segment constituting the main chain has a weight-average molecular weight of 7,000 to 100,000.本發明之整髮方法係將含有成分(A)之毛髮化妝料應用於毛髮，於50℃以上對毛髮進行賦形後冷卻至未達50℃，藉此將經賦形之髮型固定。成分(A)：有機聚矽氧烷，其係包含重複單元(1)之聚(N-醯基伸烷基亞胺)鏈段(b)經由含雜原子之伸烷基，鍵結於構成主鏈之有機聚矽氧烷鏈段(a)之Si原子的至少2個上而成：(b)之數量平均分子量為1,200~5,500；(a)與(b)之質量比為35/65~60/40；鄰接之(b)間的有機聚矽氧烷鏈段之重量平均分子量為1,300~5,500；(a)之重量平均分子量為7,000~100,000。
