Abstract The gelling properties of sepiolites from four different sources are compared with a Na-montmorillonite from Wyoming. The comparison was made on the basis of ease of gel preparation, gel viscosity and yield stress, and the modulus of rupture of slip cast bars made with kaolinite for the purpose of demonstrating that sepiolite could be used as a replacement for montmorillonite in ceramic bodies. Aqueous sepiolite gels (2 wt.% clay) were more quickly and easily prepared and had a greater viscosity and yield stress than a comparable montmorillonite gel. Also, the structure of critical-point dried sepiolite gels was examined by scanning electron microscopy and was found to be composed of interconnecting fibers in three dimensions. Slip cast bars made with sepiolite-kaolinite were weaker than those made with montmorillonite-kaolinite, but at optimum casting conditions the modulus of rupture of the sepiolite-kaolinite bars was near that of the montmorillonite-kaolinite bars.