This paper explores the criterion on the similarity of heat transfer of supercritical fluid flow in vertical pipes at different diameters by performing comparative experiments. The diameter of the pipe is chosen at 4.4 or 9.0 mm with a heated length of 2 m. The mass flux and wall heat flux are at (400 kg/m(2) s, 30 kW/m(2)), (400 kg/m(2) s, 50 kW/m(2)) (1200 kg/m(2) s, 50 kW/m(2)) with a pressure at 8.12 Wa. By measuring the inlet fluid temperature and wall temperatures, heat transfer coefficients are obtained at various inlet fluid conditions. Analytical criterion for the similarity of the heat transfer behavior is proposed and the validity of the analytical criterion is examined by comparing it with the experimental observations. It is shown that by having same length to diameter ratio and wall heat flux to mass flux ratio a similarity of heat transfer behavior was maintained both in the normal heat transfer mode and deteriorated heat transfer mode. It is also noted that the flow at bigger diameter is more susceptible to the reduction in the heat transfer due to buoyancy. (c) 2007 Elsevier B.V. All rights reserved.