The fabrication of ceramic composites based on a mullite matrix uniaxially reinforced with either high strength carbon or Nicalon-SiC continuous fibres is described. Sets of high solids contents of up to 40 vol% were prepared using colloidal silica sol with either alpha-alumina powder or colloidal boehmite as reactants for the preparation of the mullite matrix, 3Al(2)O(3) . 2SiO(2). Single-stage infiltration was used for the preparation of prepregs for laminating into composites. The composites were consolidated by uniaxially hot-pressing at 1300 or 1550 degrees C, depending on the matrix precursors and the final phases in the matrix. Highly densified composites with fibre volume fractions of 32-60% were obtained and the microstructures characterised by mercury porosimetry, X-ray diffraction, scanning electron microscopy and transmission electron microscopy.