Nb-doped WS2 nanotubes, typically W1-xNbxS2 (x less than or equal to 0.2), generated by heating Nb2O5-coated W18O49 nanorods in H2S at 1100 degreesC, contain more structural defects within the layers than do pure WS2 nanotubes. The tube tips are invariably closed. The presence of Nb appears to inhibit nanotube formation. A two-stage process is proposed to account for the observed doped nanotube growth.