Piezoresistive microcantilevers are widely applied to measurements of low forces, masses and viscosity . After surface functionalization they might be used as a biochemical sensors being capable of the intermolecular force investigation. The problem is that such sensors change its mechanical properties in the environment they operate. Therefore there is a need for a high accuracy technique being capable of measuring of mechanical properties of functionalized cantilevers operating in the target environment. We suppose that such conditions meet the analysis of thermomechanical oscillation noise. In this paper the analysis of two types of cantilevers, that might be used in bioelectrochemical measurements, was performed. We determined the cantilever deflection and force sensitivity. The spring constant was measured by three different methods: the Cleveland methods  and the thermomechanical noise analysis. The obtained results indicate that analysis of thermomechanical excitation noise is the simplest and the most reliable method for spring constant calibration of piezoresistive cantilever based sensors.