Two lanthanide borosilicate (LaBS) glasses containing 9.5 and 5.0 wt.% PuO2 prepared at 1500 °C consisted of a vitreous phase and minor crystalline PuO2 (or PuO2-HfO2 solid solution with minor HfO2) and britholite-type phases. X-ray absorption spectra of Pu LIII edge in the as-prepared and stored for various periods LaBS glasses were recorded, analyzed and compared with the spectra of crystalline PuO2. Pu in the as-prepared glass existed in predominantly tetravalent form (Pu4+ ions) but its storage in air results in partial oxidation as was seen from shift of peak energy values. In the structure of the as-prepared glass, Pu4+ ions had a co-ordination number (CN) close to 6 (˜6.3) and were located within the axially squeezed octahedra with five equidistant oxygen ions at a distance of 2.265±0.015 Å and one – at shorter distance (2.130±0.010 Å) from the Pu4+ ion. The Pu—Pu(M) distance (second co-ordination shell) was 3.675±0.015 Å. “Aging” of the LaBS glass with transformation of some fraction of Pu into penta- or/and hexavalent form was accompanied by a structural transformation.