This paper deals with model reduction of assemblies of bladed disks. Some considerations about the use of the Fourier theory to describe the dynamics of assemblies of geometrically periodic structures are first recalled. This allows to define a set of spatially mono-harmonic solutions that are used to build the kinematic subspaces in a subsequent reduction process. The main characteristics of this sector substructuring technique are then presented and discussed. Finally, the proposed methodology is applied to an industrial rotor provided by Snecma to demonstrate its capability to handle large finite element models.