The invention relates to a method and a molding core for producing a fiber composite component (34), in particular in aerospace, comprising the following method steps: introducing a core sleeve (9) into a molding tool (2) for establishing an outer geometry of a molding core (27) to be formed; filling the core sleeve (9) that is introduced with a vacuum-fixable filling material (21); applying a vacuum to the core sleeve (9) and consequently vacuum-fixing the filling material (21) for forming the molding core (27); and at least partly laying at least one semifinished fiber product (33a, 33b) on the molding core (27) that is formed, for the shaping of the fiber composite component (34) to be produced.