We propose a new technique, "position-controlled CVD using catalytic reaction," to modify pore structure. By loading the catalyst for the reverse water gas shift reaction on a support that is to be modified, He can confine the hydrolysis reaction zone to a narrow region surrounding the catalyst where H2O is generated, An anodic alumina membrane with pore size of 26 nm was used as the support. Reactant gases, H-2, CO2 and TiCl4, were led into the same side of the membrane. The effects of reaction conditions on pore modification are investigated on the basis of FE-SEM observations and permeation tests, The pore size and permeance through the membrane gradually decrease with reaction time. Deposition morphology changes with reaction conditions, such as temperature, and H-2, CO2 and TiCl4 feed rates. In some cases, particles with 0.1-1 mu m diameter are formed on the outer surface of membrane.