Starting from alumina with particle size of 0.3—0.4 μm，disk α-Al2O3 supports were prepared via colloidal filtration with a mean pore size of ca.70 nm as determined by Hg intrusion method.The polished supports with mirror-like surface were used for mesoporous membrane preparation.A stable Boehmite sol with a mean particle size of about 20 nm was successfully synthesized with aluminium sec-butoxide（ALSB）as a precursor through particle colloidal sol-gel route.Defect-free γ-Al2O3 mesoporous membranes with pore size of ca.3 nm superimposed on the disk α-Al2O3 supports were then prepared by dip-coating with the Boehmite sol and subsequently calcined in a temperature range of 400—800℃The molecular weight cut-off（MWCO）for PEG and the flux for pure water of these membranes are 2800—5300 and 11.5—25.9 L.m-2.h-1［7.6×105 Pa，(14±1)℃］，respectively，which confirms the integrity of the mesoporous membranesThe results presented in this paper provide a feasible method for the preparation of defectfree mesoporous membranes with a pore size of about 3 nm directly by coating onto macroporous Al2O3 support with a pore size of about 70 nm.