The work function at the tips of individual ZnO nanobelts has been measured by an electromechanical resonant method using in-situ transmission electron microscopy. The work function of the ZnO nanobelts is similar to5.2 eV, which shows no significant dependence on the geometrical size. Using a ZnO nanobelt as a carrier beam, the work function of a single nanoparticle of a different material has also been measured.