Oscillating heat pipes (OHP) are a promising and highly efficient heat transfer technology especially in the field of power electronics thermal management. However, conventional metal OHP do not meet the need for insulation or low coefficients of thermal expansion. In order to expand the application field and break the application limitation of the OHP technology, alumina ceramic oscillating heat pipes was designed and investigated in this paper. The alumina OHPs combine the excellent insulating, oxidation-resistant, corrosion-resistant and low thermal expansion properties of alumina ceramic with the efficient heat exchange mechanism of oscillating heat pipe technology, exhibiting great application potential. An alumina flat-plate oscillating heat pipe was prepared, 6 internal microchannels were examined using micro-CT, and the microstructure was characterized using scanning electron microscopy. The heat transfer characteristics of the OHP charged with water were investigated using a heat transfer test system. Increasing heat loads were employed to the OHP, and the operating temperature of 20 °C and 60 °C as well as the orientation varied between 0° and 90° were also introduced. The oscillation motion of the alumina OHPs were investigated, including temperature oscillations before and after startup of the OHPs, and a comparison effective thermal conductivities at various tilt angles and operating temperatures was carried out. The experimental results revealed that the heat transfer performance of the alumina oscillating heat pipe significantly increased with the increased heat loads and reached to 861.7 W/(m∙K) at 56 W. The effective thermal conductivity of the OHP was 6 times higher than that of the empty OHP at heat load of 16 W. When the orientation was 30°, the temperature oscillation instability increased, the oscillation amplitude increased, and the heat transfer performance of the oscillating heat pipe decreased. As the operating temperature increased, the stability of temperature oscillations improved, the amplitude decreased, and heat transfer performance was enhanced.