Abstract Orbital Hall effects have recently attracted significant attention for generating substantial orbital angular momentum currents in both strong- and weak-spin-orbit-coupling materials. Despite extensive theoretical and experimental progress on the orbital Hall effect, its thermal counterpart, in which a temperature gradient drives a transverse orbital current, known as the orbital Nernst effect, has remained experimentally elusive. Here, we report the first experimental evidence for the orbital Nernst effect by measuring the magneto-thermopower in the yttrium iron garnet (YIG)/Pt/CuO x heterostructures. Through systematic comparison with the YIG/Pt and YIG/CuO x heterostructures, we show that both the magneto-thermopower and the magnetoresistance for YIG/Pt/CuO x are markedly enhanced due to the contributions from the orbital Nernst effect and the orbital Hall effect in CuO x , respectively. Our experimental evidence for the orbital Nernst effect supports the orbital degree of freedom as a promising route for heat-energy harvesting and orbital angular momentum thermal transport in earth-abundant materials.