Nonsupported alumina porous membranes without pinholes or cracks were prepared by the sol-gel process using aluminum sec-butoxide as the starting material. The effects of using different PVA contents at various calcination temperatures on the characteristics of the membrane were investigated by scanning electron microscopy and nitrogen sorption porosimetry. The results after calcining at 450 degrees C for 5 hours showed that the range of pore size distributions increases with increasing PVA concentration. The active nucleus numbers of phase transition to alpha-alumina decreased as the content of PVA increased at about 1050 degrees C. The morphology of unsupported alumina membranes was affected by the PVA concentration and calcination temperature.