Isospecific and syndioselective ring-opening metathesis polymerizations (ROMP) of norbornene (NB) and tetracyclododecene (TCD), as well as their tactic (and atactic) hydrogenated ring-opened polymer products have been thoroughly investigated for the first time. In the case of NB polymerization, cis-isospecific ROMPs of NB were achieved with Mo(=O)(rac-5,5',6,6'-Me-4-3,3'-t-Bu-2-biphenolate)(2)-based catalyst (cis = 100%, isotacticity =100%). Cis-syndioselective ROMPs of NB proceeded in the presence of W(=NPh)Cl-4 center dot Et2O- and W(=N-2,6Me(2)Ph)Cl-4 center dot Et2O-based catalysts (cis = 90%, syndiotacticity =90%). Hydrogenated poly(NB)s exhibited high crystallinity irrespective of their stereostructures. The crystalline nature of syndiotactic hydrogenated poly(NB) (syndiotacticity = 90%: T-m = 130136 degrees C, Delta H = 6075 J/g, wc = 0.550.70) was close to that of conventional atactic one (meso/racemo = 50/50: T-m = 145150 degrees C, Delta H = 6570 J/g, wc = 0.65). On the contrary, isotactic hydrogenated poly(NB) was characterized by a remarkably unique crystalline nature such as high melting points (isotacticity > 90%: T-m = 160180 degrees C, Delta H = 5090 J/g, wc = 0.500.65). In the case of TCD polymerization, W(-NPh)Cl-4 center dot Et2O-based catalyst introduced cis-syndioselective ROMP of TCD (cis = 90%, syndiotacticity = 86%). Syndiotactic hydrogenated poly(TCD) obtaining from W(-NPh)Cl-4 center dot Et2O-based catalyst was entirely amorphous and soluble in ordinary organic solvents. On the other hand, atactic hydrogenated poly(TCD) showed poor solubility and semicrystallinity (T-m = 290 degrees C, Delta H < 10 J/g). In addition, Mo(-O)(rac-5,5',6,6'-Me4-3,3'-t-Bu2-biphenolate)2-based catalyst provided all-cis poly(TCD), of which hydrogenated product was completely insoluble and highly crystalline (T-m > 350 degrees C, wc = 0.65). These tendencies are in significant contrast to those of the hydrogenated poly(endo-dicyclopentadiene)s, wherein atactic polymer is amorphous and both tactic polymers are crystalline (syndiotacticity = 90%; T-m = 270 degrees C and isotacticity > 95%; T-m = 295 degrees C, respectively).