The relationship between electric fields and energetic electron precipitation for an intense substorm during the very early evening (1700-1800 MLT) was examined using balloon- and ground-based data at Syowa Station, Antarctica. The electron precipitation (>25 KeV) was implied by the Bremsstrahlung X rays measured at the balloon altitudes. A large and prompt increase in X rays occurred simultaneously with the onset of a sharp H perturbation of -1000 nT, when the azimuthal direction of the electric field changed from southwest (poleward) to northwest (equatorward). This intense precipitation occurred during the developing state of the negative H perturbation. Comparative studies of a time sequence of the electric field, electron precipitation, and auroral electrojet currents indicate that the precipitation region of intense energetic electrons (>25 KeV) in the very early evening sector was confined latitudinally to the vicinity of the region, where the enhanced westward electrojet pushes away the eastward electrojet. ¿ American Geophysical Union