  We report the Chandra discovery of an X-ray jet associated with the redshift
4.3 radio-loud quasar GB 1508+5714. The jet X-ray emission peaks ~2 arcsec to
the South-West of the quasar core. We present archival HST WFPC2 data of the
quasar field which shows no optical emission at the location of the X-ray jet.
We discuss possible emission mechanisms and give constraints to the magnetic
field and energy densities for synchrotron radiation or for Compton scattering
of the Cosmic Microwave Background radiation as the jet X-ray emission process.
