Abstract: The present invention is a composition for forming a silicon-containing metal hard mask, including: (A) a metal oxide nanoparticle; (B) a thermally crosslinkable polysiloxane (Sx) having no aromatic-ring-containing organic group; and (C) a solvent. This provides a composition for forming a silicon-containing metal hard mask that has a high effect of inhibiting collapse of an ultrafine pattern in a multilayer resist method, that can form a resist pattern having excellent LWR, that has more excellent dry etching resistance and wet removability than a conventional silicon-containing underlayer film material, and that has more excellent filling ability than a conventional metal hard mask material.