Carboxylate alumoxanes were cast onto alpha-alumina supports by slip-coating to develop asymmetric ceramic membranes. Carboxylate ferroxanes were also analyzed as possible precursor for ceramic membranes. Different support materials were studied. Membrane layers as thin as 1 or 2 mum were achieved. The effect of sintering conditions was investigated. The molecular weight cut off was evaluated for these membranes and compared to pore size data obtained by nitrogen adsorption in an effort to correlate pore size and actual performance of the membrane. Membranes were sintered at temperatures between 600°C and 1100°C. The pore sizes increased with higher sintering temperature, from 7 nm at 600°C to 10 nm at 1000°C, followed by a sharp increase due to the transformation to alpha alumina at higher firing temperatures. The molecular weight cut off showed no considerable variation up to 1000°C. These results are in good agreement with equations reported by several authors that correlate molecular weight with size.