Abstract: To better understand the convective heat transfer of the hydrocarbon fuel in horizontal tubes under supercritical pressures, an experimental study is carried out for the convective heat transfer of the aviation kerosene RP-3 in a horizontal miniature round tube. Under the working conditions of the air-kerosene heat exchanger, the aviation kerosene is heated up to the supercritical regime. The influences of the heat flux, the fluid inlet temperature, and the buoyancy on the heat transfer of the RP-3 are analyzed. It is found that the heat transfer coefficients decrease with the increase of the heat flux, and the buoyancy causes a large temperature difference of 50 K between the top and the bottom surfaces of the test tube under high heat flux conditions, which can be predicted by the non-dimensional parameter Gr_q/Gr_th. The effects of the buoyancy on the heat transfer can be suppressed by increasing the mass flux. The results may provide a technological basis for the active thermal protection of the flight vehicles to be cooled by hydrocarbon fuels.