A series of nonsupported gamma-alumina membranes were prepared by using sol-gel method. The influences of preparation parameters including acid/alkoxide ratio, water/alkoxide ratio, alcohol/alkoxide ratio, hydrolysis temperature, and calcination condition were investigated. From the experimental results, it indicated that the acid/alkoxide ratio and calcination temperature play important roles on controlling the microstructural properties of the membrane. The gamma-alumina membranes can be obtained under various hydrolysis temperatures even below 80 degrees C, and the minimum pore size occurred at about 60 degrees C of hydrolysis. With the same amounts of acid, both the particle size of the sol and pore size of the membrane obtained by the PMU route were slightly smaller than that by the DCS route. The relationship among preparation conditions, properties of boehmite sols and mircostructure of membranes were also discussed.