Metathesis polymerization of 3-fluoro-3-pentafluoroethyl-4,4-bis(trifluoromethyl)tricyclononene-7 (F-PTCN) and the properties of the resulting polymer, particularly gas permeability, have been studied. It has been found that F-PTCN exhibits high thermal stability. The gas separation parameters of the material (P(O-2) = 60 Barrer, P(CO2) = 240 Barrer) are close to those of fluorinated polynorbornenes studied previously. The newly synthesized fluorinated metathesis polytricyclononene has a lower gas permeability than metathesis polytricyclononene bearing two Me3Si groups in the monomer unit, but it is significantly superior to the latter in gas separation selectivity for some gas pairs.