A novel mesoporous material prepared using the recently reported co-assembly of anionic surfactants with organosilane groups has been studied in depth using high-resolution transmission electron microscopy (HRTEM) and electron crystallography. A three-dimensional (3D) structural solution of AMS-8 was obtained by Fourier analysis of HRTEM images, revealing a complex cubic mesocaged solid (space group Fd3m) composed of bimodal cages 3D-connected by cage windows. HRTEM images also indicate the presence of structural defects associated with the cubic close packing of spheres, while analysis by nitrogen adsorption-desorption isotherms reveals that accessibility to smaller cages may be restricted in this material. The opened and closed models of this structure derived from a combination of electron crystallography and nitrogen adsorption data are discussed with respect to the arrangement of cages and cage connectivities. Considerations of the nature of the micellar system playing part in this novel templating mechanism are discussed.