This paper reports the temperature-dependant electrical resistivity and piezoresistive characteristics of boron-doped ultrananocyrstalline diamond (UNCD), and the fabrication of piezoresistive microcantilevers using boron-doped and undoped UNCD. The devices consist of 1 μm thick doped UNCD on either 1 or 2 μm thick undoped UNCD. Over the temperature range 25-200 °C, the doped UNCD has a temperature coefficient of electrical resistance of-1.4 × 10 -3 °C -1 . The doped UNCD exhibits a significant piezoresistive effect with gauge factor of 7.5 and a piezoresistive coefficient of 8.12 × 10 -12 Pa -1 at 25 °C. The piezoresistive properties of UNCD are constant over the temperature range 25-200 °C. Microcantilevers of length 300 μm have deflection sensitivity of 0.186 mΩ/Ω per µm of cantilever end deflection. These measurements of electrical and piezoresistive properties of doped UNCD could aid the design of future diamond microsystems.