A balloon observation of auroral X-rays has been carried out by using two types of X-ray imagers. The first is a new type of imager consisting of a two-dimensional 5×5 matrix array of Si(Li) semiconductor detectors whereas the other is a one-dimensional array of 8 NaI(Tl) scintillation detectors. Both are pinhole camera type imagers. The balloon carrying these imagers was launched from Abelver, Norway, on July 5, 1985, and flew westward over Iceland. Near the location of L=5.2 at the

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... midnight during a geomagnetic substorm, temporal variations of auroral X-ray images were observed with 3-s time intervals by the Si(Li) imager. These images were confirmed simultaneously by the NaI(Tl) imager. A time sequence of the auroral X-ray images did not show a stable arc structure, but rather a localized small-scale structure with rapid time variation. The present observation suggests that localized intermittent precipitations of energetic electrons with energies of several tens keV occurred in the post-break-up phase of an auroral substorm. It is fully possible that localized energetic electron precipitations are due to the localized field-aligned electric field.