In-situ heating fluctuation electron microscopy and scanning transmission electron microscopy have been utilized to study compositional and structural heterogeneities in Zr51Cu32Al9Ni8 thin films upon annealing. Composition fluctuations are present in the as-deposited thin films. Well below the glass transition temperature, the composition fluctuations increase with annealing time. Short- and medium-range order also change with annealing temperature. The observed heterogeneities in the glass structure persist until annealing causes crystallization. The 20 nm thick Zr(51)Cu(32)A(19)Ni(8) films contain oxide layers both at the surface and the film/substrate interface with the total thickness of 7-8 nm. In-situ annealing increased the oxygen content of the whole films to about 24 wt.% after 2 h at 400 degrees C. (C) 2013 Elsevier B.V. All rights reserved.