Commercial powders of NbC (~1.20 μm), TaC (~1.10 μm), ZrC (~1.35 μm) and WC (~1.25 μm) were used as raw materials. The (NbTaZrW)C HECC was synthesized using high energy ball milling (200 rpm, 20 h, Ar gas) and subsequent vacuum sintering using spark plasma sintering (SPS) system (LABOX-325R; 2200 ◦C, 10 min; 100 ◦C/min; 40 MPa). Well-polished samples (3 mm × 3 mm × 5 mm) were used for isothermal oxidation testings.