PROBLEM TO BE SOLVED: To provide a hair cosmetic capable of imparting excellent stiffness and firmness to hairs without having the stiffness and firmness (damaged hairs by a chemical treatment or thin hairs of European, American or elderly people, or the like), and a method for treating the hair.SOLUTION: This hair cosmetic is provided by containing a silicon compound (1) expressed by general formula (1), an acid and water and showing pH 3-7. Also, the hair cosmetic is provided by consisting of a first agent containing a silicon compound (2) expressed by general formula (2) and a second agent containing the acid and water and showing pH 1-3. The method for treating the hair is provided by applying these hair cosmetic over the hair in order to penetrate the silicon compound (1) into the hair. [wherein, X is R1 or hydroxy (t) is 0-2 integer (2t+4)Xs are each the same or different X is R1, hydroxy or a group expressed by OM (t) is 0-2 integer (2t+4)Xs are each the same or different and at least one of the X is OM M is an alkali metal or alkaline earth metal R1 is a 1-6C straight chain or branched chain alkyl or alkenyl].COPYRIGHT: (C)2007,JPO&INPIT【課題】毛髪繊維、特にハリ・コシがない毛髪(化学処理等で損傷した毛髪、欧米人や高齢者の細い毛髪等)に対し、優れたハリ・コシを付与することができる毛髪化粧料及び毛髪処理方法の提供。【解決手段】ケイ素化合物(1)、酸及び水を含有し、pHが3~7である毛髪化粧料。ケイ素化合物(2)を含有する第1剤と、酸及び水を含有しpHが1~3である第2剤とからなる毛髪化粧料。これらの毛髪化粧料を毛髪に塗布し、ケイ素化合物(1)を毛髪に浸透させる毛髪処理方法。〔XはR1又は水酸基を示し、tは0~2の整数を示す。(2t+4)個のXはそれぞれ同一でも異なってもよい。XはR1、水酸基又はOMで示される基を示し、tは0~2の整数を示す。(2t+4)個のXはそれぞれ同一でも異なってもよく、Xの少なくとも一つはOMである。ここでMはアルカリ金属又はアルカリ土類金属、R1は炭素数1~6の直鎖又は分岐鎖のアルキル基又はアルケニル基を示す。〕【選択図】なし