Carbonized hallow liber membranes were prepared by pyrolyzing an asymmetric hollow fiber membrane of a polyimide from 3,3＇, 4, 4＇-biphenyltetracarboxylic dianhydride and aromatic diamines at temperatures of 500-700 degrees C under a nitrogen stream. The precursor membrane was treated in air at 400 degrees C for 0.5 h before the pyrolysis. This pretreatment was effective for improvement of gas permeance of the carbonized membranes, The carbonized membranes had an asymmetric structure with a skin layer of around 200 nm in thickness. They had the characteristics of larger permeance and lower permselectivity for inorganic gas pairs such as O-2/N-2, but this was rather preferable to the separation of olefin/paraffin. The membranes pyrolyzed at 600-630 degrees C displayed good stability and excellent performances of propylene/ propane and 1,3-butadiene/n-butane separation based on the molecular sieving.