The H-1 and C-13 NMR spectra of 1-butene chemisorbed on TS-1 and ETS-10 has been studied. The interaction of butenes with ETS-10 is stronger than with TS-1. ETS-10 is more active than TS-1 for the double-bond isomerization of 1- to 2-butene and both are highly selective. Skeletal isomerization and oligomerization are observed only at high conversion levels. The kinetic rate constants and apparent activation energies have been calculated from changes in the intensity of the NMR lines. Satisfactory agreement is obtained with corresponding values from conventional catalytic reactor data. FTIR spectroscopy reveals the presence of a significant concentration of hydroxyl groups, probably at defect sites, on the surface of both TS-1 and ETS-10. These hydroxyl groups or the Lewis acid sites generated from them on dehydroxylation at high temperatures are probably the active sites in the isomerization reaction.