In nanotechnology, small-volume metals with large surface area are used as electrodes, catalysts, interconnects and antennae1, 2, 3, 4. Their shape stability at room temperature has, however, been questioned. Using in situ high-resolution transmission electron microscopy, we find that nanoparticles can be deformed like a liquid droplet but remain highly crystalline in the interior, with no sign of dislocation activity during deformation5, 6. Surface-diffusion-mediated pseudoelastic deformation is evident at room temperature, which can be driven by either an external force or capillary-energy minimization. Atomistic simulations confirm that such highly unusual Coble pseudoelasticity can indeed happen for sub-10-nm particles at room temperature and at timescales from seconds to months.