Provided is an in-bath treatment composition for conditioning hair and maintaining hair in a long-lasting state of having volume and body. This in-bath treatment composition (100) has an emulsion structure composed of a particulate first phase (11) and a second phase (12) in which the first phase (11) is dispersed, and contains: an inorganic particle dispersion (1) composed of hydrophobic inorganic particles (2) that constitute one of either the first phase (11) or the second phase (12) and have a mean particle size of 1 nm to 15 μm in primary particles, and an oil-soluble dispersant (5) in which the hydrophobic inorganic particles (2) are dispersed an aqueous solvent (10) constituting the other of the first phase (11) and the second phase (12) a surfactant (9) for forming an interface between the first phase (11) and the second phase (12) and an in-bath treatment component included in the first phase (11), the second phase (12), or both the first phase (11) and the second phase (12). The content of the hydrophobic inorganic particles (2) is 0.01 to 20 mass% of the total mass, and the content of the oil-soluble dispersant is 2 to 71 mass% of the total mass.Linvention concerne une composition de traitement en bain pour le conditionnement des cheveux et le maintien des cheveux dans un état durable de volume et de corps. Cette composition de traitement en bain (100) possède une structure démulsion composée dune première phase particulaire (11) et dune seconde phase (12) dans laquelle est dispersée la première phase (11), et contient : une dispersion de particules inorganiques (1) composée de particules inorganiques hydrophobes (2) qui constituent la première phase (11) ou la seconde phase (12) et possèdent une taille particulaire moyenne de 1 nm à 15 μm en particules primaires, et un dispersant oléosoluble (5) dans lequel sont dispersées les particules inorganiques hydrophobes (2) un solvant aqueux (10) constituant lautre parmi la première phase (11) et la seconde pha
