Alumoxanes nanoparticles were cast onto a-alumina supports by slip-coating to develop asymmetric ultrafiltration ceramic membranes. Membrane layers as thin as I or 2 mum were achieved. The effect of sintering conditions was investigated. Membrane surface morphology was imaged by SEM and AFM. 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 and 1100 degreesC. The pore sizes increased with higher sintering temperature, from 7 nm at 600 degreesC to 10 ran at 1000 degreesC, followed by a sharp increase due to the transformation to a-alumina at higher firing temperatures. The molecular weight cut off showed no considerable variation up to 1000 degreesC. These results are in good agreement with equations reported by several authors that correlate molecular weight with size.