Abstract: The present invention concerns a method for producing a lightened SiC structure, especially for the production of a lightened mirror, with the following stages: cutting of a preform with a honeycomb-shaped structure whose voiles have an organic matrix and a fibrous reinforcement, pyrolysis of this honeycomb-shaped structural preform so as to solely preserve the carbon, silicidation of the carbon of the preform so as to obtain a microporous SiC core, infiltrating type reinforcement by means of a SiC chemical vapor phase depositing of the voiles of the honeycomb structure of the core, embodiment of a felt sheet and assembling on at least one face of the core of the embodied sheet and densification of this sheet so as to obtain at least one SiC skin on the surface of the core. The invention also concerns the structure obtained.