The Zr-Al-Gd system, as a key constituent ternary in Cu-, Gd- and Zr-based bulk metallic glasses, was thermodynamically studied in this work. Employing equilibrated alloys, the isothermal section at 873 K was established by means of scanning electron microscopy/energy dispersive X-ray spectroscopy and Xray diffraction. Phase transformation temperatures were determined by performing differential scanning calorimetry analysis on selected samples. Moreover, the microstructure of the as-cast samples was observed to identify primary solidification phases. Based on all experimental information of this work, the Zr-Al-Gd system was thermodynamically optimized with the assistance of the first-principles calculation. The calculated isothermal section, vertical sections and liquidus projection account for experimental observations satisfactorily. (C) 2015 Elsevier B.V. All rights reserved.