The colloidal way of the sol-gel process was used for elaborating nanofiltration ceramic membrane. Boehmite, precipitated in situ, was used as a precursor. The evolution of the sol as a function of the concentration was precised with the help of turbidity, viscosity and colloidal particle size measurements. No binder was added in the sol before coating which was performed by slip-casting. The gel layer was sintered using a "flash" firing treatment. The membrane was characterized by scanning electron microscopy, nitrogen adsorption-desorption and cut-off determination. The pore diameters were similar to 1 nm.