Microporous carbon membranes were prepared by a vapor-phase synthesis using furfuryl alcohol (FFA). An alpha-alumina support was coated with a sulfonic acid solution and then exposed to an FFA vapor at 180 degrees C in a closed vessel. The deposited FFA polymer was carbonized under a N-2 atmosphere. Under carbonization at elevated temperature (200-500 degrees C), micropores larger than 0.33 nm were generated. The pores shrunk at higher temperatures of 600-1000 degrees C. The pore size of the membrane carbonized at 800 degrees C is thought to be about 0.30 nm according to the gas permeation results. The FFA carbon membrane showed high separation factors for H-2/CO2 (> 22 900 at 150 degrees C), H-2/N-2 (> 2480 at 150 degrees C), and H-2/CO (> 2510 at 150 degrees C) binary gas mixtures.