Electrophoretic deposition filtration (EFD) and pressure filtration (PF) have been used to fabricate Saffil alumina fibre-reinforced mullite multilayer nanoceramic matrix composites from heterocoagulated nano-sized alumina sol particle and fumed silica powder particles dispersed in water. The surface charge properties of the particles in suspension were characterised by particle electrophoretic mobility measurements, while the effects of the short-range particle-particle interactions were observed using TEM. The heterocoagulated particle clusters were infiltrated into the multilayer Saffil fibre preforms using constant voltage EFD with varying deposition times, to establish the process parameters for the successful infiltration deposition of stoichiometric mullite. It was found that at a constant voltage of 10 V d.c., the increase in EFD deposit weight was almost a linear function of the]EFD time, while the optimum electrode separation distance was 15 mm, producing full infiltration in 4 minutes. Furthermore, for the boehmite-silica system employed in the present work, the optimum alumina/silica particle size ratio for generating discrete heterocoagulated boehmite/silica particle clusters, and hence stoichiometric sintered mullite, was 3:1. Sintering at 1500 degrees C for 3 hours produced sub-micron equiaxed mullite grains and no grain boundary glass phase, with fibre pull-out on fracture.