The mechanical properties of individual WS₂ nanotubes were investigated and directly related to their atomic structure details by in situ transmission electron microscope measurements. A brittle mode deformation was observed in bending tests of short (ca. 1 μm in length) multilayer nanotubes. This mode can be related to the atomic structure of their shells. In addition, longer nanotubes (6–7μm in length) were deformed in situ scanning electron microscope, but no plastic deformation was detected. A "sword-in-sheath" fracture mechanism was revealed in tensile loading of a nanotube, and the sliding of inner shells inside the outermost shell was imaged "on-line". Furthermore, bending modulus of 217 GPa was obtained from measurements of the electric-field-induced resonance of these nanotubes.