Diphenylacetylenes possessing fluorine atom(s) and a siloxy group (1c-i) were polymerized with TaCl5-n-Bu4Sn. Monomers 1c-f having a siloxy group at the para position of a phenyl ring produced high molecular weight polymers (2c-f) in good yields. These polymers afforded tough free-standing membranes by casting their toluene solution. Desilylation of the polymer membranes was carried out with trifluoroacetic acid to give membranes of poly(diphenylacetylenes) having fluorine atoms and hydroxyl groups (3c-f). Polymers 2c-f were soluble in various organic solvents such as toluene, CHCl3, and THF, while polymers 3c-f were insoluble in these solvents. All the polymers 2c-f and 3c-f exhibited high thermal stability. The gas permeability of most membranes in the present study (2d-f and 3c-f) were higher than those of the corresponding polymers without fluorine atoms (2a and 3a), indicating that incorporation of fluorine atoms into the polymers enhances gas permeability. The P-CO2/P-N2 permselectivity ratios of polymers 3c-f were as large as 36-48, and the points of 3c-f in the P-CO2 vs P-CO2/P-N2 plot were located above Robeson's upper bound.