This article presents convective heat transfer of hydrocarbon fuel RP-3 at supercritical pressures in vertical micro-tubes with inner diameters of 0.538 mm, 1.09 mm and 1.82 mm under heating conditions. Effects of system pressure, heat flux, mass flow rate and flow direction were experimented and analyzed with wide range of supercritical status. Also, inner diameter effect on heat transfer were compared at identical conditions. The results indicate that sharp variation of thermal properties with temperature is the key factor to influence heat transfer. Normal, deterioration and enhancement heat transfer phenomena generally occur in turn along with dimensionless position. Moreover, Nusselt number variation shows good agreement when the contrast temperature T-b/T-p, is lower than 0.80 and Bo* = 1.0 x 10(-8) could be the critical point to evaluate buoyancy influence. At last, two well-predicted empirical correlations of Nusselt number are proposed for downward and upward flow heat transfer in 1.09 mm tube. (C) 2017 Elsevier Ltd. All rights reserved.