  We report a Chandra observation of the z=3.395 radio galaxy B2 0902+343. The
unresolved X-ray source is centred on the active nucleus. The spectrum is well
fit by a flat power law of photon index of Gamma~1.1 with intrinsic absorption
of 8x10^{22} cm^{-2}, and an intrinsic 2-10keV luminosity of 3.3x10^{45} erg/s.
More complex models which allow for a steeper spectral index cause the column
density and intrinsic luminosity to increase. The data limit any thermal
luminosity of the hot magnetized medium, assumed responsible for high Faraday
rotation measures seen in the radio source, to less than ~10^{45} erg/s.
