Nano‐mechanical oscillator (NMO) based on amorphous carbon nanowhisker (CNW) with nanotraps for resonant weighting of nanoparticles in range of mass (10−14–10−15) g is presented. NMO with nanotraps is fabricated on the top of tungsten tip using focused electron beam technique. For resonant weighting the gold nanospheres are captured under the exposure of an electron beam by nanotraps locate on the top of CNW. Jump of gold nanoparticle to the nanotrap and oscillations of CNW are visualized using scanning electron microscope (SEM). The NMO amplitude‐frequency characteristics are calculated via automated numerical analysis of the sequence of SEM images obtained during the oscillations frequency sweeping. In order to calibrate the resonance mass detector based on CNW with nanotrap the gold nanosphere with diameter of (170 ± 5) nm and mass of (49.6 ± 9.2) × 10−15 g is weighed in vacuum.