Gadolinium calcium oxoborate (GdCOB) is a nonlinear optical material that belongs to the calcium-rare-earth (R) oxoborate family, with general composition Ca4RO(BO3)(3) (R3+ = La, Sm, Gd, Lu, Y). X-ray photoemission was applied to study the valence band electronic structure and surface chemistry of this material. High resolution photoemission measurements on the valence band electronic structure and Gd 3d and 4d, Ca 2p, B 1s and O 1s core lines were used to evaluate the surface and near surface chemistry. These results provide measurements of the valence band electronic structure and surface chemistry of this rare-earth oxoborate. (c) 2005 Elsevier B.V. All rights reserved.