Gadolinium oxide nanoparticles of diameters <5 nm were uniformly decorated on the surfaces of multiwalled carbon nanotubes which were subsequently used as templates to fabricate gadolinium oxide nanoparticle-decorated multiwalled carbon nanotube/titania nanocomposites. The prepared nanocomposites were evaluated for the photocatalytic degradation of methylene blue under simulated solar light irradiation. Higher photocatalytic activity was observed for the gadolinium oxide-decorated multiwalled carbon nanotube-based nanocomposites compared to the neat multiwalled carbon nanotube/titania nanocomposite and commercial titania. This improvement in photocatalytic activity was ascribed to the gadolinium oxide nanoparticles supported at the interface of the carbon nanotubes and titania resulting in efficient electron transfer between the two components of the composite. Total organic carbon (TOC) analysis revealed a higher degree of complete mineralisation of methylene blue (80.0 % TOC removal) which minimise the possible formation of toxic by-products. The photocatalyst could be re-used for five times, reaching a maximum degradation efficiency of 85.9 % after the five cycles. The proposed photocatalytic degradation mechanism is outlined herein.