We present a highly sensitive nanobalance based on a piezoresistive cantilever beam with a porous silicon element. Measurements of a shift of the cantilever resonance frequency allow estimation of adsorbed substance weight (e.g., gas, steam) with single nanogram resolution. Applications of such a device include humidity and gas detection. Moreover, a cantilever beam with a porous silicon element enables combined investigations of mechanical and adsorption properties of porous silicon. The fabrication process of the device has been described as well. (C) 2003 American Vacuum Society.