The ring-opening metathesis polymerization (ROMP) of norborn-2-ene (NBE) and cis-cyclooctene (COE) was initiated with well-defined Grubbs-type initiators, i.e., RuCl2(CHPh)(PCy3)(2) (1), [RuCl2(PCy3)(IMesH(2))(CHPh)] (2), and [RuCl2(3-Br-Py)(2)(IMesH(2))(CHPh)] (3) (MesH(2) = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene, PCy3 = tricyclohexylphosphine, 3-Br-Py = 3-bromopyridine). Reaction of the living polymers with O-2 (air) resulted in the formation of aldehyde-semitelechelic polymers in up to 80% yield, depending on the initiator and monomer used. To proof aldehyde formation, the terminal aldehyde groups were converted into the corresponding 2,4-dinitrophenylhydrazine derivatives, and the structure of the hydrazones was confirmed by NMR and IR spectroscopy. This simple methodology was then used for the functionalization of ROMP-derived monoliths prepared from NBE, 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo-endo-dimethanonaphthalene (DMN-H6) and (NBE-CH2O)(3)SiCH3, to yield aldehyde-funtionalized monoliths. The extent of aldehyde formation was determined by hydrazone formation. Up to 8 mu mol of aldehyde groups/g monolith could be generated by this approach. Finally, these aldehyde-functionalized monoliths were used for the immobilization of trypsin. Excellent proteolytic activity of the immobilized enzyme was found both under batch and continuous flow conditions.