  We present a comparative study of the unfilled CoSb3 and FeSb3 skutterudites
and report on their compressibility studied by high-pressure synchrotron X-ray
diffraction. The equation of state for FeSb3 was received for the first time.
The third order Birch- Murnaghan isothermal equations of state were fitted to
the experimental data in the pressure ranges atm-34 GPa for CoSb3 and atm-14
GPa for FeSb3. Bulk moduli of 95(5) GPa and 86(4) GPa have been obtained for
CoSb3 and FeSb3, respectively. The bulk modulus of FeSb3 is in a contrast by
about 30% with literature value obtained indirectly. Anomaly was observed in
the diffraction pattern of CoSb3 at the pressures 34.4-39.6 GPa which is most
probably reasoned by structure transition.
