A compact Kirkpatrick-Baez mirror system (KB) has been specially designed at ESRF for the ID21 SXM. This KB is based on elliptically shaped, fixed-focus Ni coated mirrors (Zeiss, Germany). It achieves a spot size of 0.35 x 0.7µm2 with a photon flux of 7.1010 photons/s. The compact design of this KB ensures high mechanical and thermal stability, and a short focal length which allows a high source demagnification. The advantages of the KB configuration are its higher photon flux and its achromaticity which is preferable for µXANES.