Tungsten-based catalysts induced syndioselective ring-opening metathesis polymerization (ROMP) of endo-dicyclopentadiene (DCPD) to produce a new class of crystalline polymer. Various tungsten(VI) imido chloride complexes of the type W(=N-R)Cl(4)circle(Et2O)(n) (R = Ph, 2,6-Me2Ph, alpha-naphthyl, 2,6-i-Pr2Ph, Et, n-Bu, n-Hex, cyclohexyl, adamantyl; n = 0 or 1) were prepared, which in combination with Et2Al(OEt) efficiently induced ROMP of DCPD. W(=N-Ph)Cl(4)circle Et2O and W(=N-Et)Cl-4-Et2O promoted cis- and syndioselective ROMP of DCPD, and the following hydrogenation provided a new crystalline polymer, syndiotactic hydrogenated poly(DCPD), which was characteristic in high melting point and in high crystallinity (T-m = 270 degrees C, Delta H = 52 J/g, w(c) = 0.61). The syndioselectivity of the polymerization could be controlled in the range 30-80% by the suitable choice of those tungsten imido catalysts. These are the first examples of well-designed binary catalysts that are effective in the syndioselective ROMP of DCPD.