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Despite significant interest in their functional properties, the mechanical behavior of high-entropy oxides (HEOs) is not well studied, particularly at elevated temperatures. Bulk (Co,Cu,Mg,Ni,Zn)O (transition metal (TM)-HEO) samples were deformed under compression at applied stresses and temperatures ranging from 5 to 31 MPa and 600 to 850 °C, respectively. All of the deformation conditions result in creep stress exponents of n < 3, indicating that TM-HEO exhibits superplastic deformation. A transition from structural to solution-precipitation-based superplasticity is observed during deformation above 650 °C. Additionally, TM-HEO exhibits shear-thickening behavior when deformed at stresses above 9 MPa. The formation and behavior of a Cu-rich tenorite secondary phase during deformation is identified as a key factor underpinning the deformation mechanisms. The microstructure and phase state of TM-HEO before deformation also influenced the behavior, with finer grain sizes and increasing concentrations of Cu-rich tenorite, resulting in the increased prevalence of solution-precipitation deformation. While complex, the results of this study indicate that TM-HEO deforms through known superplastic deformation mechanisms. Superplasticity is a highly efficient manufacturing method and could prove to be a valuable strategy for forming HEO ceramics into complex geometries. 

High‐entropy oxides (HEOs) are being extensively studied for various functional applications, but there is limited research into the mechanical behavior of these materials, especially at elevated temperatures. Bulk (Co, Cu, Mg, Ni, Zn)O (transition metal (TM)‐HEO) samples are formed into dome shapes at 800 °C and 70 kPa. Deformation experiments and finite element analysis (FEA) reveal that TM‐HEO has a creep stress exponent ofn = 0.6, indicating that TM‐HEO deforms through superplastic deformation and exhibits shear‐thickening behavior. Comparisons of experimental strain rates to those calculated using existing superplasticity mechanism models signify that TM‐HEO deforms through grain boundary sliding accommodated by a solution‐precipitation mechanism from a secondary phase. A Cu‐rich tenorite phase, commonly observed in the grain boundaries of TM‐HEO, is proposed as the secondary phase facilitating deformation. It is important to highlight here that the superplastic deformation behavior in TM‐HEO is active under modest temperature and pressure conditions, as noted above. Low‐temperature superplastic deformation will provide a powerful method of manufacturing HEO ceramics into net shape parts, greatly expanding their potential applications.