The preparation and characterization of silicon nitride based microfiltration ceramic membranes are described. The ceramic membrane filters had a composite asymmetric structure consisting of a mechanically strong porous silicon nitride support coated with one or more thin active sialon/silicon nitride layer(s). Three methods of synthesizing the thin membrane layer with pore sizes smaller than 1 mu m were compared. One route used liquid phase pressureless sintering of an ultrafine inorganic powder, a second was based on the pyrolysis of an organometallic polymer precursor, and the third was the nitridation of a vacuum evaporated silicon thin him. Phase compositions in the ceramic filters were determined by X-ray diffractometry and energy dispersive analysis. Microstructural characterization was performed using scanning electron and confocal laser microscopy. Property evaluation included measurement of density, porosity, pore size, water permeability and water flux.