Ultrashort single-walled carbon nanotubes loaded with gadolinium ions (gadonanotubes) have been previously shown to exhibit extremely high T1-weighted relaxivities (>100 mM-1s-1). To further examine the effect of nanoconfinement on the relaxivity of gadolinium based contrast agents for magnetic resonance imaging (MRI), a series of ultrashort single-walled carbon nanotube (US-tube) materials internally loaded with gadolinium chelates has been prepared and studied. US-tubes were loaded with Gd(acac)3ﾷ2H2O, Gd(hfac)3ﾷ2H2O, and Gd(thd)3. (acac = acetylacetone, hfac = hexafluoroacetylacetone, thd = tetramethylheptanedione) The longitudinal relaxivities of the prepared materials determined at 25ﾰC in a 1.5 T field were 103 mM-1s-1 for Gd(acac)3ﾷ2H2O@US-tubes, 105 mM-1s-1 for Gd(hfac)3ﾷ2H2O@US-tubes and 26 mM-1s-1 for Gd(thd)3@US-tubes. Compared to the relaxivities obtained for the unloaded chelates (<10 mM-1s-1) as well as accounting for the T1 reduction observed for the empty US-tubes, the boost in relaxivity for chelate-loaded US-tubes is attributed to confinement within the nanotube and depends on the number of coordinated water molecules.